[DiapDealer]

You're welcome! I've noted the libgl1-mesa-dev package in the official github build instructions, so thanks for reporting your errors. Hopefully the efforts of people like you and philja will make things easier for others.

Your video card should be fine. I just forgot that the OpenGL dev headers and includes might not be present on systems that don't do a lot of building. Especially on those distros that split the dev stuff out by default in their packaging.

Note that some plugins will be looking for PySide6 when used with Qt6-built Sigil. We left PyQt behind on our other platforms when we switched to Qt6. Unfortunately most Debian/Ubuntu-based distros don't have Pyside6 packages in their repos. There are a few workarounds for this if you run into any problems.