I have posted here that my X-T4 freezes for about 10 seconds after turning it on. After the pause, everything works as normal. I called Fuji tech support in New Jersey this morning and discussed the problem. After being told that (a) they had not heard of similar problems and (b) that usually this type of problem is 'user error' , I am shipping my X-T4 to them for repair under warranty. I've upgraded firmware MANY times on X-T1, X-T2, and X-T3 cameras without issue. This is not a new process to me. The X-T4 shows that v 1.02 firmware is installed. I do NOT think this is 'user error'.
I'm reporting here in case it may be of use/value to others.
Glad my X-T3 is still a reliable workhorse.