Does anyone know how I can overcome this?
As far as I know, you can not buy or swap real Bitcoin for Altcoin or Altcoin for real Bitcoin on trust wallet because, like other users already said, Bitcoin is a stand alone coin, Bitcoin's blockchain does not support smart contracts like it is with Ethereum and Binance smart chain, Bitcoin you can swap or buy with altcoin on trust wallet has to be either..
-Ethereum version which you can buy or swap from uniswap
-Binance smart chain version which you can buy or swap from pancakeswap... etc.
A solution i can recommend to you is to download chainge wallet, chainge wallet is non-custodial wallet with built in decentralized exchange with also a cross chain feature which can enable you buy or swap real Bitcoin to altcoin and also swap or buy real Bitcoin with any Altcoin listed on the wallet, you can also cross chain Bitcoin to and from various chains if you want ...you can find the app on Googleplay store and iphone app store.
Below is what the Bitcoin page on the app looks like.