Also, how much RAM does the old PC have? Windows 10 allegedly requires "1 GB for 32-bit or 2 GB for 64-bit," but I suspect that performance would be better with 8 GB.
I'm going to suggest that you don't need an extremely powerful CPU or GPU. You probably do want a recent CPU (e.g., Intel 11th or 12th generation - or AMD equivalent) – but it's not clear that you'd gain much from chasing the fastest clock speeds, or Core i9 over Core i5/i7.
It sounds like...
You said that "No moving parts (if you buy a Mac w an M1 or M2 chip.)"
The M1 Mac Mini, M1 iMac, 13" M1 MacBook Pro, and 13" M2 MacBook Pro all have fans. "No fans" is specifically a MacBook Air thing.
USB-A is a "single-purpose" connector. It can carry USB data and a small amount of power.
USB-C is a "Swiss Army Knife" connector. It can carry
USB data
DisplayPort data
Thunderbolt data
Substantial amounts of power (up to ~100 watts) – enough to charge many laptops, or to power accessories...
Apple now has abandoned not just internal optical drives, but internal hard drives. All current Macs have internal SSDs … and the only ones that can even take internal hard drives are the Intel-based Mac Pros (with the aid of third-party products).
If SSDs continue to get larger and cheaper...
I agree that optical drives are now marginal for backup, but they still have applications:
Importing music from your CD collection for use on your computer, phone, etc
Creating DVD-Video and Blu-Ray-Video discs containing family photos and videos