What's the best way to sell ~50 BTC these days?
- open an account at a reputable exchange that supports fiat transfers to your jurisdiction and go through KYC (this can take a while).
- transfer a small part to your BTC wallet at said reputable exchange and exchange it into some fiat of your choice.
- have it transferred to your fiat account and check that it all goes through.
- then do the rest. Note that legitimate exchanges have daily/monthly withdrawal limits that you'll probably hit, so you might have to spread over time. (Might want to split it across multiple exchanges to spread ops risk.)
Or: Go to Hong Kong or Moscow or Cambodia and go to any of the dodgy bureau de change's there, transfer BTC to the wallet address they specify, wait several hours, and take out the cash (probably worse rate than an exchange). (If you value your life and property, I would pick Hong Kong among the suggestions above.)