I know of Maestral. It uses the public Dropbox API which means any files Dropbox deems ‘grey area’ (think console BIOSes but there is a ton of stuff that gets erroneously flagged) refuse to sync.
I’m not a first time Linux user, and I can somewhat deal with these pain points, but recommending Linux to layman people, especially when telling them “it’ll work smoother and be more bug-free than Windows and macOS” is just setting them up for a world of technical pain.
You are experienced and I share some of the pain, so I won’t beat the point in. But I do think every OS has its pain points and advantages — and linux has a unique adaptability that just about anyone can find their niche in. Nothing is bug free but it might just be smoother, given advertising has infected the major corporate Oses.
Anyway, in general:
If you like Mac, use Gnome. That is the default in Ubuntu.
If you like Windows, use KDE. That comes default in Kubuntu.
Ubuntu is debian-based, so you need to use packages that support that if you use Ubuntu. Dropbox and Spotify both have installation instructions for using it on Ubuntu and, when I used those instructions, everything worked fine.
There is also Maestral for dropbox: https://maestral.app/
It is an open source dropbox client. Needs less permissions and the performance is good, it works well in linux but I had some issues on arm based Mac. Used it a year or two ago so perhaps it has gotten better.
I’m willing to bet there exists an open source solution that integrates with the Spotify SDK as well.
Sleep, power management, etc all work well for the userfriendly focused Ubuntu distros. It was a major pain point for me for a while many years ago when I started, but I found that KDE Ubuntu distro and it made everything a lot easier for me migrating to linux. Give it a shot.
I do think Valve involvement will help the landscape a lot, I just hope it doesn’t bring must-haves that are proprietary.