Hi, you should use
highway=footway
footway=sidewalk

for pedestrian only sidewalk or

highway=path
bicycle=designated
foot=designated
footway=sidewalk
surface=***

for a combined bicycle-pedestrian one

Hi, you've added name to the building, but the data doesn't say what it's used for. I recommend adding

Check OSM wiki
and see if these tags are applicable or maybe something else
osm.wiki

industrial=warehouse
office=construction_company
craft=roofer
building=warehouse

You can add tags at the bottom section when you select the building

Please keep your changesets local next time and upload each country separately, thank you.

Thanks for a thorough answer.
I recommend to remove name, description and website from the building and add add office=research or office=company for the node.

You can do this at the bottom section "Tags" when you select the node or the building.

You can also move the node closer to one of the staircase entrances or whatever entrance you are using. Just don't put it too close to the edge or those maps which want to display it, may have not room for the text.

Hi, please use name in a local language as a default name

Hi, features should only be added once. Currently it's added both as a node and on the building.

This looks like an apartment block, I assume people live there and they are not part of GoGoNano. So you should remove the tags added to the building.

Nothing describes what it is except description text. I recommend adding office=research or office=company

Is this just a legal address, or does GoGoNano really function there?

It's called block heater
https://en.wikipedia.org/wiki/Block_heater

I don't know anything about them, but see if

socket socket:=**

or power outlet
power=outlet

are applicable

Hi, do Germans still use "Kreis Harrien" name? Harju kreis is a historical name, but Harjumaa borders don't event match with it. I'd remove it.

Hi, is the screen reachable from a wheelchair? What about top shelves?

Hi, uturn restriction should probably also be removed. Nothing prevents it I think.

I've changed all mentioned parking lots to public access. Haven't seen any signs which would make them non-public. Be careful next time!

While multipolygon can be used to represent areas with holes using inner and outer members, a multipolygon can represent multiple disjointed areas by having only outer members. It's better supported by data consumers than a site relation, so I think we should use it where we can.

Site has an advantage when you need a relation having not only areas, but for example a node and an area, which is not the case here.

I think it's better to use multipolygon relation as it's better supported

And for the airport's address you've put a Russian street name. We don't really translate addresses even if it was in a correct tag. I'll revert this changeset.

*It's like => it's likely

building addresses are mostly managed automatically. It's like housenumber added to Kurmäe hostel will get erased since it's missing in official sources.

Hi, be careful, you've accidentally changed bus station's name

Thank you! Added it to actual school amenity too, so that it won't be just on a building.

and why is this
way/875901109
access=customers?
Customers of what?

Hi, why have you made these
way/307428684
way/307425971
parkings private?