I believe the minimum amount of information that must be stored is the last block, the UTXO set, and the timestamps of the blocks since the last difficulty adjustment.
This UTXO set and timestamps could be secured by adding a hash of them to every block. Something like this has been proposed in the past.
I think you're talking about "UTXO commitment", where it require miner to submit merkle root of UTXO set. It's never implemented to Bitcoin Core due to various reason (such as amount of data need to be hashed), but Bitcoin Core have similar feature called "UTXO snapshot"[1].
Do you think the size of the blockchain will bloat more than my calculation suggests just 20 years from now?
Why don't you just show your calculation step by step?
[1]
https://blog.lopp.net/bitcoin-node-sync-with-utxo-snapshots/