Spoiler: Bitwig works on a Surface Pro 6 tablet with Linux (yes, it turns out it’s a 6 and not a 5 as I thought).
This is what I did, taking as a reference Installation and Setup · linux-surface/linux-surface Wiki · GitHub 
- Create a Windows recovery USB drive (because I had no access to the original password, recovery key, Microsoft account…)
- Go through all the Windows updates available (I ended up with Windows 11 from 2022 or something like that).
- Create a plain Ubuntu USB drive.
- After Ubuntu was installed, enable the Surface Linux kernel for touch etc.
- Install Ubuntu Studio Installer, enable only the audio configuration tool, and then run it for the audio configuration tweaks.
- Enable performance mode (although balanced seems to do fine too?)
- Install Bitwig and enable the Tablet UI (although small display at 200% seems to be fine too; I need to play around more with both modes).
And that’s it. As a simple instrument it works. I hear some crackling with complex Grid presets but the system performance display doesn’t show clipping spikes, so maybe even that can be solved. In any case, the presets of various I have tried so far sound well, and many Grid presets sound too. And the whole experience is responsive, not sluggish. I haven’t tried to load complex projects or complex effects chains because that’s not why I want Bitwig in a tablet anyway.
Not bad at all for an old tablet that Microsoft tells you to dump!