Actually incorrect. (Not legal advice, but read the licences yourself.)
The previous version of TrueCrypt (7.1a - the one you'd actually want to fork because it could still encrypt things), was still under a licence that'd allow you to fork it as long as you didn't call it TrueCrypt (or anything resembling it).
That was basically inherited from E4M. It's an ugly licence, however.
https://diskcryptor.net/ might be worth looking into (this is not a recommendation, I have not audited it). It's certainly cleaner - TC's kinda ugly inside, with a decade of maint cruft.
The previous version of TrueCrypt (7.1a - the one you'd actually want to fork because it could still encrypt things), was still under a licence that'd allow you to fork it as long as you didn't call it TrueCrypt (or anything resembling it).
That was basically inherited from E4M. It's an ugly licence, however.
https://diskcryptor.net/ might be worth looking into (this is not a recommendation, I have not audited it). It's certainly cleaner - TC's kinda ugly inside, with a decade of maint cruft.