I can write that I have 333 BTC or any other number that comes to mind, but it will still be just a made-up story - just like yours. If for some reason (although I don't see why) you want to prove that you have 33 BTC in your possession, then sign a message from your BTC address where you keep them.
Exactly... it reminds me of fake YouTube millionaires who
"buy
" a new exotic car in almost every video just to attract viewers.
"Money attracts money" – this scheme never gets old.
Then they wait for questions like "How do you earn?" so they can sell their BS (books, videos, seminars, etc.) - all worthless.