For completeness sake I would only add that a nation-state actor or an organized crime org with access to an unethical CA can generate certs for any site and perform the MITM. CA's sometimes get caught operating this way. One method to mitigate this is to periodically check the fingerprint of the cert for the site you are talking to.

Here is one way using openssl:

   for i in $(echo -e "news.ycombinator.com ycombinator.com www.ycombinator.com"); do echo -en "${i}: "; openssl s_client -servername "${i}" -connect "${i}":443 < /dev/null 2>/dev/null | openssl x509 -fingerprint -noout -in /dev/stdin; done|sort -k2 -t"=" | awk '{print $NF "\t" $1}' | column -t

  Fingerprint=22:05:8D:96:A0:F7:9B:8F:B8:1D:0F:74:EC:4B:76:8F:84:B0:42:49  www.ycombinator.com:
  Fingerprint=5D:70:F0:DC:E0:AF:67:A0:8F:BC:2F:B8:49:F0:79:5D:8B:FF:49:93  news.ycombinator.com:
  Fingerprint=C4:A6:FF:38:83:13:31:DC:14:01:3D:05:E8:3B:29:95:FD:AE:9B:0E  ycombinator.com:

One could diff the output in a script then send an alert if there is a diff from one test to the other. If doing this factor in expiration and test from multiple locations. Meaning you can expect the cert to change some time before it expires, hopefully.

   openssl s_client -servername news.ycombinator.com -connect news.ycombinator.com:443 < /dev/null 2>/dev/null | openssl x509 -noout -dates

  notBefore=Sep  7 00:00:00 2021 GMT
  notAfter=Oct  8 23:59:59 2022 GMT

Another mitigating control is public key pinning but very few organizations do this any more. It is just too risky operationally. Another method is to limit what CA's you trust but this is not practical for most organizations. e.g. You have a specific purpose system that only talks to Specified_Bank and that Specified_Bank only uses Specified_CA, you can strip out all other CA's from your trust store and/or manually pin their public key in your system accepting the risk connections will break when they update their cert without coordinating with you.