Disable HTTPS upgrade?

That's RFC 9460. Firefox has support but it's apparently disabled by default. Chrome supposedly has support too, but I can't find any documentation that it is actually enabled and working (or any flag to turn it on).

Browsers have long resisted adding any DNS lookups to the dependency chain for loading a page because they say people are extremely latency sensitive. It sounds like platform support for arbitrary DNS record types has been problematic too.

Hence they've ignored a number of records that have been proposed to improve security (e.g., TLSA).

I think that RFC was developed with their input to try to address their needs, so it's really sad to see it not be enabled. Though it's at least implemented, which is progress, I guess?