At least for one, or two of my previous phones, and some time ago, the “the bootloader is unlocked” warning was removable by flashing an alternative logo.bin.
Is something similar possible for the FP3(+)?
Thanks for your help
I will answer it myself.
Just close the bootloader and everything is well (it will reset your data. be prepared).
After that, my LOS booted normally.
My experience on the pixel 3a was, that closing the bootloader pushed me back to stock rom.
So , I expected this to happen on the FP3, too.
May be, I missed something with the pixel, may be, this is default for this phone.
Now, after reinstallation, everything works well for me.