You'll definitely want to use the HWE kernel, so that you have a chance of getting a kernel which can decently use the different architecture/layout of the CPU.
It can be installed like this:
apt update && apt install linux-generic-hwe-20.04 -y && reboot now
I'd suggest cautiously testing that server, because ubuntu 20.04 is already quite "old" regarding current hardware support and thus I am not sure how well the CPU scheduling will work for the new CPU even with the 5.15 kernel.
In any case, please report your results here after testing. Thanks!