I played X4 a lot, years ago but on a much weaker system. Now I boot it up and even the logo/intro screens are choppy. Performance analysis tells me the game is barely using CPU and GPU. Tried starting a brand new game, and even the tutorial is unplayable.

My system
Lenovo Legion 5 pro 16ACH6H
AMD Ryzen 7 5800H with Radeon Graphics 3.20 GHz
RAM 16,0 GB
NVIDIA Geforce RTX 3070 for laptops (yes the game is set to use this, and I've disabled the integrated graphics card)
Win 11 home

Any ideas? Is it a known issue?

Indeed it is. Unfortunately X4 is badly optimized and extremely CPU demanding: around the web there are many thread about the performance issues with the game.
I suggest you to read this thread to get some suggestions about possible solutions (different users report different solutions). The performance issues can't probably be completely eliminated, anyway you should try to play with the settings in order to mitigate the problem.

Thank you, that helped! The solution for me seems to be running it in compatibility mode (windows 8)

Thanks for posting your solution: this might help other users.

I'm happy of having helped you. Enjoy the game!