Entering these buildings as a node does not make sense, because they are not displayed in openstreetmap.org, e.g. https://www.openstreetmap.org/node/10924985434.
Since the JOSM is already used, on the top right under the category 'Layers', if a 'Data Layer' has already been downloaded, and below it the 'Image Layer' e.g. Bing has been selected, this can be changed by clicking on the eye, in this case the value 'Gamma' (3rd from the top) by moving the slider in light or dark.
If the Buildings tool has not yet been integrated, under Settings (slider icon), in "Extensions" (puzzle icon), select "buildings_tools" there and confirm. So you can then simply draw in a building by 3 clicks. With the "X"-button you can change the shape of the building. ...
Greeting vogelfreier/Rüdiger

Translated with deepl.com