This part you can skip if you're not the type whose brain gets stuck on "why are you doing that": I have a catalog I use for art reference images, so it mainly takes advantage of the Lightroom hierarchical keyword feature. Sometimes I want to visually annotate a particular image. LRC does not support this oft-requested feature, so I use Photoshop and "Edit Original" for this purpose.
Windows 10, LightRoom Classic 10.1
Inside Lightroom, in Library in grid view, I select a photo and press Ctrl-E to edit in Photoshop, selecting "Edit Original". I make change in Photoshop, Ctrl-S to save. Alt-Tab back to Lightroom, it has not detected change. Verify file timestamp is changed on disk, use Explorer to verify disk contains changed image. OK, right-click on folder in LRC, select "Synchronize Folder...". Fails to detect any changes.
When this happens, I seem to be able to reliably get Lightroom to at last notice that an image has changed by doing something like zooming in or editing. Presumably, anything that gets Lightroom to go back to the disk for the actual complete bits will do the trick.
Of course, if Synchronize Folder simply never worked, Adobe would've found the problem and fixed it by now. So, in fact, it does sometimes work in this scenario. Leaving me with the puzzle of can I figure out a reproducible sequence of events that produces the problem? Difficult.
Just switching to Develop shows the correct, edited image, and then switching back to Library still produces the same out of date thumbnail.
Trying to guess why I get to see the bug so much more often than presumably normal people do, I note that all these photos were taken with a camera phone (Samsung Galaxy Note 4). Also, at the time I Ctrl-E to Photoshop, there are often no edits in place other than keyword assignments. Hierarchical keywords have been applied in bulk (at a minimum, to assign the name of the book the image was taken from). Grasping at straws here.
Sometimes when I return to Lightroom, it instantly rotates the image 90 degrees for no apparent reason, but still is using the out of date image. If I then zoom to force it to go to disk, it not only displays the correct image but undoes the inexplicable rotation that it previously added.
In this particular catalog, the bug appears so reliably that I haven't been able to figure out any guesses about what's different on those rare photos the bug does not appear.
If I edit the same photo a second time, the changes seem to reliably appear as soon as I switch back to Lightroom.
Alt-Tab back to Lightroom, it has not detected change.
This would indicate a problem with the Preview cache not updating. I might suggest you delete the ...Previews.LRDATA folder and then allow LrC to re-build the Previews. Some info here- PREVIEWS CORRUPT
I then zoom to force it to go to disk,
In fact- Photoshop will have already done this when you [Save] the image in Photoshop. It is only the Preview in LrC that is not updating!
Synchronize Folder simply never worked,
It never will for this purpose!- Synchronize Folder is only designed to import 'new' files that are not already in the catalog. The [Ctrl+E] Edit in Photoshop, is working with a file already IN the catalog. (Synchronize Folder can also delete file previews of files that are shown as 'missing' in the catalog!)
The "Rotation" problem is a weird one I have not seen. Try a Preferences reset- PREFERENCES RESET
I followed your workflow with a TIF image (Edit 'Original'), added some text, Saved, and my Lr preview updates ok- as did all the Virtual Copies of the TIF 🙂 -