Since one year I'm using a MacBook Pro 13 upgraded to Catalina in October. I use the Mac to program same embedded module via RS232 (different adapters with different chips, e.g. FTDI) and it is still working.
Last Monday I changed to a new MacBookPro 16. I used a backup and all worked proper, but I can't connect to any USB-to-Serial adapters. I got the same
error  could not open port /dev/tty.usbserial-xxxx: Resource busy ...
I tried to reinstall all corresponding drivers, but without success.