You wrote:
"... Photos had started hanging (revolving rainbow wheel) when I performed actions such as clicking on the "People" album or "Places" album etc. Also more often than not it would not import new photos from my iPhone 11 (latest iOS). Sometimes it would not play videos from the main library. ... "
The symptoms you described in your original post are indicating problems with the media files in your Photos Library. You will be seeing this, if the library contains damaged media files or media in a legacy format, that Photos can no longer handle after a system upgrade. Such problems cannot be fixed by a library repair. Trying to repair the library can even make it worse, because the library repair can get stuck, when it tries to rebuild the library and wants to create previews and thumbnails, but can't, because the files cannot be processed. That is why we need to make a backup of the library, before we risk to repair it.
You need to identify the image files or videos that Photos can no longer process and remove them from the library. Export them as the original file, then delete them from the library, then try to find some third-party software to convert the problematic items to a more compatible format, before you try to reimport them.
How to use the Photos Repair Library tool on your Mac - Apple Support
You may want to restore your library from your backup copy (duplicate it, if you have enough free storage). The problem is, if you open the backup copy, Photos might try to repair it as well. It will be safer to use a copy and not to open the saved version. To check for incompatible items start with videos where you noticed that they will no longer play. Export the suspicious items (File > export > Export unmodified original), then import hem to a new, empty library. If there is a problem with the video, Photos will give a warning, that the file is not supported.
Any item that cannot be imported into a new, empty test library needs to be converted to a more compatible format.