What are these very formal, old-fashioned words (wherein, thereof etc.) called? [closed]

Solution 1:

Many of the words you list are used as legalisms

2: a legal term or rule

Lawyerspeak, and legalese are also used to describe such terms.

Aforementioned and aforesaid in contracts:
https://www.adamsdrafting.com/aforesaid-and-aforementioned/

Henceforward in the Emancipation proclamation:
https://legal-dictionary.thefreedictionary.com/Emancipation+Proclamation

Notwithstanding in contracts:
https://weagree.com/weblog/notwithstanding-is-a-tricky-one/

The simple ones often get used in regular speech, but the more complex variants are almost always found in contracts and such. They're like XOR, EOR and NOR used mostly by logicians and programmers.