How to migrate myServer license?

If it's permanent licensed, it is fine as is.

How about switching to new hardware, the Pi 4 i had mysever on seems to have died. Will I have issues getting my license working on a different Pi. Also is it worth upgrading too Pi 5 from a 4.

Thanks

We remove the license from the old hardware and enable it on the new hardware.
Licensing is with the hardware.