I recently bought a new 1 TB NVMe SSD (970 Evo Plus) to upgrade from my current 256 GB M.2 SATA SSD. The current disk is LUKS encrypted using the default options were when I originally installed ...

Its probably just the boot order. Go into the BIOS and make sure its trying to boot from the correct hard drive first. If you aren't sure what drive you are supposed to boot from, just switch whatever ...