Noble titles are a poor comparison since they're the rare example where there actually is an exclusively-male root form. For most words the root form is neuter, and both male-only (if it exists) and female-only forms require an affix.

Properly, a male lich is "werlich" and a female lich is "wiflich" (unlike other words the /f/ sound is not likely to disappear); the plurals add "-en". But generally sex is irrelevant for undead{cn} so the neuter form by far predominates.

"lichess" is an abominable mixture of German and French roots ... so naturally it is indistinguishable from the rest of English.

It's "Libre" chess, as in "Free (and open source)" chess