Changing motherboard

I tried the suggestions and they didn't work for me, but that might be down to me.
I eventually resorted to shorting the motherboard jumpers and got into the BIOS normally. I was surprised to find that time and date were still set and even more surprised to find that CSM was still disabled, fTPM was enabled and secure boot was enabled, as was ACHI. I had expected a full reset to defaults. This motherboard is a bit strange as it does not have a boot sequence adjustment, but I could disable boot from the SSD.
I put the W11 DVD in and did a successful clean install of W11 PRO and activated it via my Microsoft account, and everything seems normal, no quibbles about the processor and now fully up to date. To get the screen resolution correct, I had to manually install drivers from AMD.
Seasons greetings, by the way and thanks everyone.