I just wanted to jump in here real quick and mention another slightly different option for HSA use that hasn't been mentioned yet...
One of my biggest areas of concern for my FIRE plan is bridging the gap between my retirement age and 59.5. So, if I end up coming up short with my brokerage account to bridge that gap, I'm planning on withdrawing my HSA funds to reimburse me for my past medical expenses to give me some additional (tax free) income during those years before I reach 59.5. Obviously, the ideal scenario is that I have plenty of money in my brokerage account to bridge that gap, but if not, the HSA is a nice tax-free way to get some additional cash flow. And if I do end up having enough in the brokerage account, then I would just leave the HSA money alone and use it after age 65.