When I upgraded my SSD in my old 64gb model to just a 256gb, I had to reinstall all my games from scratch, including D4. Nothing would work otherwise that I had on my old SD card. After that I had no problems. When I get back from a concert this evening I can look and see what version of proton my D4 is running so that I can say with certainty that it is working and let you know
Just did mine tonight. Just shy of 10y by maybe a week, been getting ready for the switch for weeks. Browsed right up to the end, deleted, and no looking back