Hi genieen16 and thank you for replying. I have an iMac, 2019 vintage, running Monterey 12.0.1. I mostly post photos to Facebook and Twitter, but I also have an Instagram account that I rarely use and I just tried and got the same result when trying to post there; all the photos, doubled and tripled and none of the separate albums. When I simply click on Photos in the taskbar I do get all the albums.
I have some of my own albums in Photos, and I set up six shared albums so my husband can look at relevant for him photos. On the iPad (3rd generation Air) I have the same situation slightly different: when I go into Photos I can see all my albums, shared and unshared, but when I go to post a photo on a site I only get everything and the non-shared. On my iPhone6 I can't see the shared albums at all in Photos, but when I go to post a photo I get everything and the non-shared albums.

Here is a screen shot of what I get on the iMac when I want to post a picture. Notice that there are no albums showing in the left sidebar.
I hope this is making sense!
What I would really like to have is to be able to see the albums on the iMac when I want to post a photo, but all I get is this ridiculously long list of teeny thumbnails, all doubled and tripled.
Thank you again, and Happy New Year! I'm off to eat little brown baked things and quaff something.