if you just show bank statement with the money in and out of an exchange and provide the trade history that's all they need really to comply with proof of funds.
even if you acquired crypto through staking or mining,︀ it will show on the blockchain being minted by the contract so its even easier.︁
the problem is if you acquire crypto from shady/illegal money/activities or if you lost paper︂ trail of your purchase. even then for this you just need to be a bit︃ creative to make a transaction that wont require proof of funds, its not easy but︄ its not the end of the world either, just need to travel a bit to︅ less stringent jurisdiction really.
what's important is to be aware of this and to plan︆ in advance otherwise your funds will be stuck and just lost really.