Google Photos Sync?

Another option to consider would be to copy your photos to your PC, then try to backup from there. No idea if that will be successful (and it would still take a loooooong time for all of those files to copy), but it may be worth a try: https://support.google.com/photos/answer/6193313?co=GENIE.Platform=Desktop&hl=en

Was thinking of doing that now. I have a phone backup from 3 weeks ago when my last phone broke. I guess I could upload those, and then do the remaining ones manually once a month until I've done a real clearout?
 
Sure, that would be a good approach. At least you could test it and see if it works.
 
The pc backup said even more lol, before I left it for work, it said 40k out of 90k backed up. I definitely don't have that many, not sure why the high numbers. I have a lot but not close to 100k...
 
Whoops - duplicates?

With iCloud it won't allow duplicates.
With OneDrive you can. And I detest how Samsung is in its own sub-directory. But I turned on OneDrive when Samsung stopped backing up photos.

You said you have a 3 week old backup - locally.
The need for uploading to Google?
Would a NAS drive suffice?

Is Google seeing an upsurge in users updating/uploading?
 
The pc backup said even more lol, before I left it for work, it said 40k out of 90k backed up. I definitely don't have that many, not sure why the high numbers. I have a lot but not close to 100k...

If you backed up images using the Windows File Explorer feature, that usually backs up every single image on the phone -- including cached images used by apps and other system images. So there can be a heck of a lot more images than you had intended.