Why YSK: It appears several Lemmy Instances are flagged as suspicious and at least 1 instance intentionally using the name of ransomware. A couple of the big enterprise monitoring suites (Fortiguard, ZScaler) will flag your account and may end up with you being pulled into an office for an explanation, or worse.
TL;DR: Keep browsing to your local instance at work for now.
Its worth noting, you cant actually MITM most traffic without device acess. To MITM my lemmy traffic, you would need either a copy of the certificate and private key of for example lemmy.world, which they would never willingly provide, or you would need to get a valid certificate from a CA for lemmy.world, which you could never get without verifying ownership of the domain.
If you are using a company owned device to browse Lemmy, then 100% they can very easily install a custom Root CA and make their own certificates, and you should assume all your traffic is monitored. But if they allow BYOB or for your phone to be on the network, then they would be unable to see that traffic without you being able to tell, because you would get certificate errors.
But if they allow you to install a VPN, then just use TOR with a TOR bridge and you wouldnt have issues, because they cant tell its VPN / TOR traffic akaik