This is a question for Master Daniel Lowrie, in regards to the "Remote Access" episode of the CompTIA PentTest+ course.
At 22:10 in the episode you executed the following command on your Linux Mint VM:
ncat --exec /bin/bash -vnl 9999 --ssl
When I attempt to perform this on my Kali Linux VM, I get the following output and subsequent error:
Ncat: Version 7.70 ( https://nmap.org/ncat )
Ncat: Generating a temporary 1024-bit RSA key. Use --ssl-key and --ssl-cert to use a permanent one.
Ncat: SHA-1 fingerprint: 00B1 F002 9F1A D830 230A D7FF 269D C9A2 1870 34F4
Ncat: SSL_CTX_use_certificate(): error:140AB18F:SSL routines:SSL_CTX_use_certificate:ee key too small. QUITTING.
Can you please advise how to correct and proceed?