I know people would dismiss this, but I'm going to try to make the case for Qt - I'm currently converting my note-taking app to mobile and it's going very well.
I heard this repeated many times. You can create closed-source Qt apps without paying any money. You cannot statically link, though; you must obey the LGPL license; that is all.
And yes, you cannot use commercial modules, but that is kinda expected.
Yes, Qt is mature and high-quality software. If you’re doing OSS, then Qt is truly a no brainer. The amount of C++ you have to write is truly minimal, and it’s not “raw” C++. There’s a lot of tooling and libraries. You can target web now too, and QML is legitimately good.
If KDE can develop a high performance stable desktop, you can design whatever.
I have been involved in two non-trivial Qt mobile apps. Never again.
I don't know what your experience is, and I mean no offence or anything, but the only people I have seen who were happy with Qt for mobile development were people who had never tried to do it with a modern language, like Kotlin.
With Compose Multiplatform and Kotlin Multiplatform, you can write a cross-platform app in a modern language, and that is far better than C++.