Please work more carefully:
https://tools.geofabrik.de/osmi/?view=areas&lon=-73.73747&lat=45.35639&zoom=16&baselayer=Geofabrik%20Standard&opacity=0.95&overlays=duplicate_node%2Csingle_node_in_way%2Cduplicate_segment%2Cway_in_multiple_rings%2Cintersection%2Cintersecting_segments%2Cring_not_closed%2Ctouching_rings%2Crole_should_be_inner%2Crole_should_be_outer%2Cinner_with_same_tags%2Cways%2Cduplicate_node%2Csingle_node_in_way%2Cduplicate_segment%2Cway_in_multiple_rings%2Cintersection%2Cintersecting_segments%2Cring_not_closed%2Ctouching_rings%2Crole_should_be_inner%2Crole_should_be_outer%2Cinner_with_same_tags%2Cways
And please do not overlap areas with identical key natural or landuse.

Das sind keine Multipolygone:

relation/18810840
relation/18808048
relation/18806833

Multipolygone sind für Flächen. Sie haben nur Polygone (geschlossene Ringe) als Mitglieder!

Your updates have probably failed:
https://tools.geofabrik.de/osmi/?view=areas&lon=-63.76396&lat=44.62007&zoom=13&baselayer=Geofabrik%20Standard&opacity=0.95&overlays=duplicate_node%2Csingle_node_in_way%2Cduplicate_segment%2Cway_in_multiple_rings%2Cintersection%2Cintersecting_segments%2Cring_not_closed%2Ctouching_rings%2Crole_should_be_inner%2Crole_should_be_outer%2Cinner_with_same_tags%2Cways%2Cduplicate_node%2Csingle_node_in_way%2Cduplicate_segment%2Cway_in_multiple_rings%2Cintersection%2Cintersecting_segments%2Cring_not_closed%2Ctouching_rings%2Crole_should_be_inner%2Crole_should_be_outer%2Cinner_with_same_tags%2Cways

Bitte Wege nicht mehrfach mit widersprüchlichen Eigenschaften erfassen:
https://tools.geofabrik.de/osmi/?view=routing&lon=11.75209&lat=49.36923&zoom=18&baselayer=Geofabrik%20Standard&opacity=0.95&overlays=duplicated_edges
https://tools.geofabrik.de/osmi/?view=routing&lon=11.75240&lat=49.39493&zoom=16&baselayer=Geofabrik%20Standard&opacity=0.95&overlays=duplicated_edges
https://tools.geofabrik.de/osmi/?view=routing&lon=11.77846&lat=49.37604&zoom=18&baselayer=Geofabrik%20Standard&opacity=0.95&overlays=duplicated_edges

Please fix:
https://tools.geofabrik.de/osmi/?view=areas&lon=-73.69261&lat=45.40418&zoom=18&baselayer=Geofabrik%20Standard&opacity=0.95&overlays=duplicate_node%2Csingle_node_in_way%2Cduplicate_segment%2Cway_in_multiple_rings%2Cintersection%2Cintersecting_segments%2Cring_not_closed%2Ctouching_rings%2Crole_should_be_inner%2Crole_should_be_outer%2Cinner_with_same_tags%2Cways%2Cduplicate_node%2Csingle_node_in_way%2Cduplicate_segment%2Cway_in_multiple_rings%2Cintersection%2Cintersecting_segments%2Cring_not_closed%2Ctouching_rings%2Crole_should_be_inner%2Crole_should_be_outer%2Cinner_with_same_tags%2Cways

By the way: JOSM provides a validation tool which detects such issues before data upload

Wenn Du Teile von Multipolygonen löschst, kümmere dich bitte auch um den übrig gebliebenen Rest:
Stand vor deiner Bearbeitung: https://overpass-turbo.eu/s/1ZaN
Stand nach deiner Bearbeitung: https://overpass-turbo.eu/s/1ZaK

Multipolygone kennen nur member mit den Rollen "outer" oder "inner"

Es ist nicht vordringliche Aufgabe von OSM, ein bestimmtes Kartenbild zu erzeugen, sondern möglichst realitätsgetreue topographische Daten zu erfassen. Und ein Acker oder Wiese endet nunmal spätestens am Straßenrand.

Was hat denn das way/49043465 mit der Stadtmoosach zu tun. Und warum tagged man das als etwas, das es nicht ist? Etwa nur weil einem die Signatur in der gerenderten Karte gefällt?

… und dabei das Multipolygon zerstört https://osm.mapki.com/history/relation/16229671

Und was ist mit dem Rest relation/6797225#map=13/48.83071/15.61738 ?

Bitte sorgfältiger bei der Bearbeitung der Grenzrelationen vorgehen: https://tools.geofabrik.de/osmi/?view=areas&lon=13.16100&lat=47.15816&zoom=9&baselayer=Geofabrik%20Standard&opacity=0.95&overlays=duplicate_node%2Csingle_node_in_way%2Cduplicate_segment%2Cway_in_multiple_rings%2Cintersection%2Cintersecting_segments%2Cring_not_closed%2Ctouching_rings%2Crole_should_be_inner%2Crole_should_be_outer%2Cinner_with_same_tags%2Cways%2Cduplicate_node%2Csingle_node_in_way%2Cduplicate_segment%2Cway_in_multiple_rings%2Cintersection%2Cintersecting_segments%2Cring_not_closed%2Ctouching_rings%2Crole_should_be_inner%2Crole_should_be_outer%2Cinner_with_same_tags%2Cways

Hat das einen Grund, warum Du das Äußere Polygon way/158529665 gelöscht und damite das Multipolygon https://tools.geofabrik.de/osmi/?view=areas&lon=7.91286&lat=53.64590&zoom=14&baselayer=Geofabrik%20Standard&opacity=0.95&overlays=duplicate_node%2Csingle_node_in_way%2Cduplicate_segment%2Cway_in_multiple_rings%2Cintersection%2Cintersecting_segments%2Cring_not_closed%2Ctouching_rings%2Crole_should_be_inner%2Crole_should_be_outer%2Cinner_with_same_tags%2Cways%2Cduplicate_node%2Csingle_node_in_way%2Cduplicate_segment%2Cway_in_multiple_rings%2Cintersection%2Cintersecting_segments%2Cring_not_closed%2Ctouching_rings%2Crole_should_be_inner%2Crole_should_be_outer%2Cinner_with_same_tags%2Cways verstümmelt hast? Ähnliches hattest Du bereits mit der MP-Relation https://osm.mapki.com/history/relation/2123680 gemacht.

Please look at https://tools.geofabrik.de/osmi/?view=areas&lon=5.75558&lat=50.47892&zoom=12&baselayer=Geofabrik%20Standard&opacity=0.95&overlays=duplicate_node%2Csingle_node_in_way%2Cduplicate_segment%2Cway_in_multiple_rings%2Cintersection%2Cintersecting_segments%2Cring_not_closed%2Ctouching_rings%2Crole_should_be_inner%2Crole_should_be_outer%2Cinner_with_same_tags%2Cways%2Cduplicate_node%2Csingle_node_in_way%2Cduplicate_segment%2Cway_in_multiple_rings%2Cintersection%2Cintersecting_segments%2Cring_not_closed%2Ctouching_rings%2Crole_should_be_inner%2Crole_should_be_outer%2Cinner_with_same_tags%2Cways

Please do not add new highways (way/1323243005) where one already exists. Adjust the tags on existing ways instead. Do not add fake landuses to indicate track properties. Add suitable properties (mtb:scale=*) to the corresponding road section instead.

War das Absicht, dass Du den äußeren Ring https://overpass-turbo.eu/s/1UYO des Multipolygons https://overpass-turbo.eu/s/1UYR gelöscht hast?

Is there a reason to change relation type=superroute to type=boundary?
https://osm.mapki.com/history/relation/7650451

Was ist das für eine Art von landuse? Ist das irgendwo dokumentiert?
relation/18294094

Wo ist hier der Einfluss von Wasser (siehe relation/18292107)?:
relation/18292107

What I found were two incomplete multipolygons and two untagged ways. So much for the small error.

I didn't delete any of your work, nor did I add a single new node.

What I did was that I added the members of one multipolygon to the other. I then deleted this multipolygon because it had become superfluous. I combined one of the untagged ways with another one, which deleted it. I completed the remaining multipolygon with the remaining untagged way and added the necessary tags for the Lac Vital.

Wird das mal zu Ende gebracht:
https://tools.geofabrik.de/osmi/?view=areas&lon=7.10356&lat=50.79953&zoom=14&baselayer=Geofabrik%20Standard&opacity=0.95&overlays=duplicate_segment%2Cway_in_multiple_rings%2Cintersection%2Cintersecting_segments%2Cring_not_closed%2Ctouching_rings%2Crole_should_be_inner%2Crole_should_be_outer%2Cinner_with_same_tags%2Cways