I recently bought a new M4 MacBook running Tahoe 26.5.1. I've been having a lot of syncing problems with Dropbox. I had an existing 70 GB of data on my previous computer, and the first thing I did was try to sync on the M4. It took about two days for the sync to finish and for the green circles to appear next to all files and folders. That's a very long time compared to previous computers I've installed dropbox on, such as my Windows 11 computer and my M2 MacBook running Sequoia.
I hoped that once it finished syncing, it would work okay. But I continue to have sync problems. The app says "Syncing…" almost all the time rather than "up to date". I have set "New files available offline," but it takes several hours for the green circle to appear next to new files.
I don't know if this true, but a Google search says that a lot of people are having trouble on Tahoe, including syncing issues.