Marie_3078 wrote: ... The only thing I wonder is if I can somehow incorporate iPhoto into Photos to make one library of all my pictures?
You're right-- you have to get them together! iPhoto is no longer supported, so, while those pictures will not get lost, they will get harder and harder to view and organize.
Your other problem is that you can't use the same Photos Library on Monterey and on Sonoma. The databases are not compatible-- if you load a Monterey Photos Library on Sonoma, it will "update" the Library to work with the new features, and then it will no longer open in Monterey. So don't try it! The only way to view pictures in a Photos Library on two different systems is to synchronize them with iCloud. It looks like you're doing that, so stick with it.
I think that in Monterey, the iPhoto Library opens in Photos with the structure intact-- is that right? But I think I remember that Monterey does not merge Libraries, at all. As I mentioned earlier, I would use the 3rd party app, PowerPhotos ($30), on your iMac to merge the iPhoto Library with the Photos Library to preserve its structure, or use PowerPhotos to merge the new (iPhoto) Photos Library with the other Photos Library. Either should work, and you could try both. The PowerPhotos people are very kind and very experienced if you need help.
As you mess around with these two Libraries, you should disconnect from iCloud in Photos Settings>iCloud. Get the Library set up as you want, and then re-connect. And before you do any damage 😵💫, be sure you have backups!