There is Ton on Unstoppable wallet but its tokens like USDT and others are not yet there. I do not want to use wallet like Trustwallet for it because it is close source.
Sadly, sometimes you need to compromise if you want to store altcoins or their worse half - shitcoins. If there is no support in open-source and trusted wallets, you are left with holding your alts in an exchange (a bad solution) or compromising and using a closed-source non-custodial wallet (a slightly less bad solution). If I had to make that decision, I would pick the latter.
That is true but Unstoppable wallet is supporting many blockchains. It is supporting Ethereum, Binance Smart Chain, Binance Beacon Chain, Solana, Polygon, Avalanche, Tron, Optimism, Arbitrum, Fantom and Gnosis. Those chains have their own tokens which are many. I think they will soon support Ton soon.
I am not dealing with the altcoins, I use those chains for USDT or USDC. USDT on many exchanges have $0 fee which is the reason I want to use it in addition to other chains that I have already. Optimism is low in fee on exchanges, I will still be using it for frequent transactions.