Is ETH Mainnet the only chain on which Txs are tracked?

I’m afraid I will be over taxed anytime I do a cross chain transfer/bridge from a chain which the IRS is not monitoring/collecting data for to one that it is. E.g…
Imagine you move $1000 of ETH to BSC or some other chain. Imagine the cost basis of that ETH were $500, triggering a capital gain of $500 at the point of transfer/bridge (which the IRS will view as a sale.)
Now I’m going to assume you don’t gain or lose any money on the $1000 when it is on the second blockchain… If IRS cannot track activity on other chains yet, if you move that money (still $1000 worth of crypto) back to ETH in the future, would it not be treated as 100% income with a 0 cost basis? Because how could they determine cost basis if they can’t tell where the money came from. So you effectively get taxed on the original disposition ($500 cap gains) and then the $1000 upon bridging it back, which means you get taxed on $1500 of cap gains and income, or 3x the amount of the true gains/income. Is there anyway to avoid this besides avoiding cross chain Txs/bridging all together? I can manually take note of all bridge Txs, but it’s going to be a major pain in the butt.