A lot of rules that apply to v5 transactions should also apply to v6. For example:

• [NU5 onward] Any SIGHASH type encoding used in a version 5 transaction MUST be the canonical encoding
of one of the defined SIGHASH types, i.e. one of 0x01, 0x02, 0x03, 0x81, 0x82, or 0x83. (Previously, undefined
bits of a SIGHASH type encoding were ignored.)

I assume that should also apply to v6.

There are a lot of similar instances if you search for "version 5 transaction".