Vielen Dank für die Hinweise. Ich habe sie jetzt wie beschrieben umgesetzt.

access=designated makes no sense (according to my understanding and according to the wiki). Also it looks unlikely to have a designated bike path in the middle of the forest on tracktype = grade5.
Would be good if someone could check what makes sense here.
If someone repairs it, please close the note I created at the point.

maybe tagging with storage_tank? This wiki page at least mentions heat. But we should know than in which medium the heat is stored.
osm.wiki/Tag:man_made%3Dstorage_tank

I added some of these information to the wiki: osm.wiki/WikiProject_Iceland/Cycleways#Rules_for_cycleways_in_Reykjav.C3.ADk

When we get to highway=footway with bicycle=designated (osm.org/way/92620069) it gets a bit too confusing (footway ⇒ foot=designated!) I would say. As a map drawer I wouldn't know how to understand that.

Hi Tómas,
thank you for your detailed comment.
I understand you in the following way: in Reykjavik/ Iceland concerning foot/bike paths (except the new big double versions): even though the sign only says foot, cycling is legally allowed and it is commonly done.
(I wouldn't hesitate to cycle their as well.)
That also means that the data does not include information on which sign is there.
Coming from Germany where I also wouldn't hesitate to cycle on such a path but wouldn't tag it as allowed since it is not allowed, it's a bit surprising.

I've put this information into the wiki: osm.wiki/WikiProject_Iceland/Cycleways#Rules_for_cycleways_in_Reykjav.C3.ADk
Maybe someone will read it.

Concerning the new double bike paths, maybe you have an answer to my question there: https://forum.openstreetmap.org/viewtopic.php?id=70367

This street imagery is pretty good! I wonder if it could be incorporated into osmose the same way as Mapillery data, or just imported into Mapillery.

Thank you!

Thank you for your advice! I incorporated these things in changeset #57597413.
About the names: it's good to have someone italian to look over that. I just copied what I read what was written.

Mit Sicherheit. An diesem Baum wollte ich nichts ändern, muss wohl ein JOSM-Bedienfehlers eines Mapper-Neulings sein.