I don't know if you've tried Plasma but it's an excellent DE that hits your "seamless synchronization" and "better UX than MacOS" requirements. Sandboxed apps

I don't know if you've tried Plasma but it's an excellent DE that hits your "seamless synchronization" and "better UX than MacOS" requirements. Sandboxed apps are a no-go on a productive desktop. Have you tried using Snaps? They're sandboxed by default, and it's extremely annoying having barriers in the way sharing data between them. Sandboxing is the sworn enemy of composition. It's like keeping all the interior doors of your house locked. Clearly defined platform / guaranteed to work: Linux-the-kernel provides a binary-compatible ABI. This is entirely sufficient, if you bundle everything including libc. If you don't want to do that, well glibc is backwards-compatible so you can just build against some reasonably old version of glibc and it'll work on any recent distro. This isn't some obscure method - lots of software is binary-distributed this way (Firefox, Blender). Easily make a commercial product: well, I'm currently using Pointwise and Mathematica on Linux, so it doesn't appear to be that hard.