I totally agree with this, even on KaiOS, now with the 3.0 version of the OS and the new firmware that pushes on some devices, they lock the devices so no way to sideload even using the webIDE. It's just their way to push even more f ads on the devices. Keep in mind that the OS on Linux phones is a bit slow - there are some videos on YT, one is this: https://www.youtube.com/watch?v=fCKMxzz9cjs - (UBports seems the most fluid there) I was ready to get the Pinephone, but I think it's better for me to get some older device that is supported by eg LineageOS.
Librem 5, pinephone and pinephone pro.