Absolutely do a clean install. Rule of thumb is motherboard change = clean OS install. you can freely switch CPUs on same motherboard with no issues but switching platforms without a clean install is asking for trouble.

While running Windows on an HDD will certainly make everything very slow and it’s a fact, it will not introduce freezes(at least long ones) and crashes. Sounds like your Windows installation might be borked or your hardware is not stable.

If I were you, I would start with a clean Windows install, including the complete wipe of your system drive.

Yep, that too! There is an enormous amount of lower end hardware used in such kinds of equipment.

There’s always a market for a sub $50 CPU. Office PC, Grandma’s HTPC, a starter computer for your kid, etc.