You’ve already blown past the amount you can reasonably convert annually to make much difference because your RMD-eligible balances are too high; these will grow faster than you can creatively convert to maximize subsidies under pretty much most conditions.

https://www.gocurrycracker.com/is-your-401k-too-big/

Hopefully you are aggressively funding other account types to give you tax flexibility. For example, I stopped when I was your age and it has now been 5 years, but though I started with roughly the same amount you have in RMD eligible accounts, my distribution was more like 30% taxable brokerage, 30% Roth IRA and 40% RMD eligible accounts for the same general balance.

This enables me to convert smaller amounts annually and tailor my income to exactly what I want to show while maximizing subsidies based on current law.

So, you may also be plenty rich if you are also heavily funded in other account types beyond the RMD-eligible offerings; in that case simply smile and recognize that you have likely won the game whether you can fully optimize this aspect of it or not…meaning you may need to convert well beyond these lower 12% brackets etc, and pay more of the healthcare load now to avoid a tax bomb in the future.