In another
thread, philja mentioned their trials and tribulations that can offer you a lot of insight into building Sigil on Ubuntu (on which Pop OS is based). The snags you mentioned so far were both mentioned (and resolved) in
that thread.
The seemingly missing qt6-5compat-dev package on older Ubuntu distros like Jammy was solved by using the libqt6core5compat6-dev package instead. See the following post in that other thread:
https://www.mobileread.com/forums/sh...80#post4372580
The Qt6::qwebengine_convert_dict issue was solved by installing the qt6-webengine-dev-tools package. See:
https://www.mobileread.com/forums/sh...98#post4372798
I expect your build will follow their Ubuntu Jammy experience so you would do well to follow that thread from the 2nd page on :
https://www.mobileread.com/forums/sh...=357115&page=2
The github instructions for building Sigil with Qt6 on Linux are still based on newer versions of Ubuntu (23.04 and higher) than you're using. Jammy (22.04) will work, but there's some massaging necessary. Linux Qt6 packaging changed pretty drastically after 22.04.