Transaction fees currently make up a tiny sliver of the mining rewards, and this seems likely to be even more the case the more ways there are to exchange it off chain (like trading ETFs). https://mempool.space/graphs/mining/block-fees-subsidy
If bitcoin becomes a world reserve currency like maxis think it will, then in a late-stage bitcoin scenario, the main chain would have such a high demand, and thus high enough fees, that it would serve more as a settlement layer where side-chains take up the majority of user activity, which collects enough in fees to push a transaction to the 'base' bitcoin chain, using the metadata to provide cryptographic proof of its activities (to avoid fraud), kind of like ETH l2's.
