MacBook Pro M1 Thunderbolt port speed discrepancy

It is certainly possible the right USB-C port is damaged. When repairing my organization's laptops, I find many of them have damaged USB-C ports. Unfortunately it is very hard to see the damage by viewing the contacts through the port opening so it is very easy to miss some signs of damage.

You can try rotating the USB-C connector 180º upside down to see if that makes any difference. If the port is half bad, then sometimes this can make a difference. The 1,000Mb/s sounds like it may only be connecting at USB3 speeds of 10Gb/s which is the maximum USB3.1 speed supported by Apple on this laptop. (Yes USB4 is supported, but it is handled differently than USB3). I would try rotating the cable connector on the left side to see if it affects the speed just in case the issue is with the cable or drive enclosure.

have you enabled TRIM for this and other external drives?

If not, your drive could be slowing because you have written every block at least once, and it can't unload the deleted data without TRIM.

https://eshop.macsales.com/blog/31619-how-to-execute-trimforce-command-with-your-owc-ssd/