Do I need to reinstall Windows when switching from Intel to AMD?

You don't strictly have to reinstall, but I would for a motherboard and CPU platform change. A clean install gives you a fresh starting point rather than carrying over old drivers and settings that could complicate troubleshooting later.

Back up your files first, then reinstall Windows and your applications. You can reuse the same drive, but make sure the backup is somewhere else before wiping it.

You can try the existing installation first. Windows may adjust to the new hardware, and if everything works, you could save yourself the reinstall. It's a convenience versus cleanup choice, not a guaranteed failure if you keep it.

Have a backup either way. If you run into problems you can't sort out, a fresh install is still an option.

The motherboard change is the main reason people recommend starting fresh. It brings a different chipset and other onboard hardware, so Windows will need appropriate drivers for the new board.

Whether you reinstall or not, check the new motherboard's support information for its drivers. If you keep the old install and something behaves oddly, the previous hardware configuration is one possible thing to investigate, not proof that the install is broken.