Hi Emma!
So this only happens when the PS5 is booting (in the boot animation)?
Then there is something wrong on firmware level based.
Just wondering, did you tried another TV? Just to be sure.
What you can try is to update the PS5 it's firmware and see if that solves it, if not, then it will be very difficult to fix this. I even advise to contact Sony at this point. Make sure that you also share your TV model with them.