Mac mini M4 internet speed drops dramatically after startup

After a couple of weeks of working OK, my Mac Mini M4 (512gb 24gb) internet connection went to almost zero in seconds after startup. It connected only in the 300mps range, and then quickly dove down to 4 or 5 mps. That happened both via wireless connections and ethernet. My 2017 imac, which the mac mini was suppose to replace, connects in the 900s for both wireless and wired.

After trying a few fixes with Apple, they advised me to return it. Anyone else have this issue? Do you have slower connections with the mini than with other devises?

[Re-Titled by Moderator]