It's pretty easy to do - sell for fiat on any exchange that trades in it, and deposit fiat to your linked bank account. Unless you're unloading millions, then you're better off doing an auction.

Serious question - is there any doubt that one can successfully convert BTC to fiat? I've done it many times on the major exchanges (Gemini & Coinbase) with absolutely no problem.

because past $100K it becomes difficult rising to impossible from every person I've directly spoken to