I'm with #6. Bring all photos down to Mac storage. Create a photo album or several to then load with the photos you really want on your phone at all times, sync those photo albums. You'll probably go from 378GB down to maybe 1 or 2GB MAX or so. And that will be hand-picked, ALL favorite photos.
Else, the game you are playing is going to lead to needing more and more very expensive Apple storage in each new iPhone and in iCloud.
And if you don't have the space on the Mac, buy yourself a big external drive (dirt cheap in 2024) and save your Photos library there. Then, 378GB won't be hogging up huge space on EITHER internal drive.
If you have some special need to have access to all 378GB at all times, get them download, dump iCloud, invest in a Synology or other NAS and thus own your own cloud storage device. Since you won't charge yourself relatively steep fees every month, it won't take many months for this option to cost less than what you are doing. And a NAS can be used for MANY other things too.
Another tip: purge the near duplicates. If this is- for example- 50 selfies that are slightly different from each other, pick the 1 or 2 best ones and delete the rest. That will very quickly get a massive library down to manageable size. I see this all the time in that huge library "problem" with friends seeking help.
And one more: if the library is a big mix of different categories of photos- like work, family, documents, etc- consider creating several libraries for each category and then load each up with the photos that you want in them.
Else, Apple will be thrilled to way overcharge you- over and over again- to carry (what may be) every photo you've ever shot all the time.
