How can I get iCloud Drive to actually sync and download files?

Environment: MacBook Air 15-inch M2, 2 TB storage, macOS 15.0.1 (24A348). Internet speed: 360 Mbps.

I recently had to reset my laptop (because attempting to open files that synced with iCloud Drive crashed the application attempting to open them), so now I'm attempting to resync (i.e. download) all my files from iCloud Drive, but for some reason while it synced a few (after I manually requested it download the folders), now it seemingly won't sync any, apart from the occasional file.

How can I get iCloud Drive to actually sync in a timely manner? I don't understand why it can't work.

Also, has anyone moved from iCloud Drive to a different cloud storage solution, if so, what would you recommend? (I highly value the security that comes from keeping everything inside the Apple ecosystem, but I've lost days of productivity to this now, and potentially even more days if it refuses to sync.)

Thank you for your help and advice!