One more possibility that nobody has mentioned yet is to see if the motherboard has a serial port header. Many motherboards still have an actual serial port that doesn’t show up on the edge as a 9-pin, but on the board as a 10-pin header. You can get the header adapter for a few dollars
(or maybe in your junk drawer). https://www.google.com/search?q=serial+header+adapter

Also, I just plugged in a PL2303 based adapter to a CentOS 8 machine yesterday to connect to a Cisco serial console and it just worked.
–Rich