In most developed markets (US, EUR, GBP etc) you can by inflation-linked long-dated government bonds which effectively will shield you from inflation if you are certain the notional value is more than large enough that you don't really need any real returns for the rest of your life.
+1.
With the excess capital above what’s needed to fund future expenses (i.e., future life expectancy in years x annual post-FIRE expenses + end-of-life needs such as healthcare or required minimum estate value) you can get very aggressive with your investments in an attempt to maximize your legacy.
Example:
You need $50k/year in FIRE.
You are 40.
You want to plan for living until 100.
You expect end-of-life healthcare costs of $300k.
You want to leave at least $1,000,000 to each of your two children.
If you have more than 60x50,000+300,000+2,000,000=$5,300,000 you can put that all in TIPs and put whatever is left over into tech, Bitcoin, private equity, or whatever you want to gamble on... or just keep it in TSM funds.