Here is a snip from The Lightroom Queens book the Adobe Lightroom Classic MissingFAQ book related to the 9.2 update. It may give some insight to Adobe's thinking on the issue.
"If you've used defaults extensively, you may notice that you can no longer set defaults by ISO. Once upon a time, when the defaults feature was first released, the noise
reduction sliders required different settings for different ISO values, so ISO-specific defaults saved a lot of time. Over the years, however, Lightroom’s noise reduction has become a lot smarter. Behind
the scenes, noise profiles have been created for almost all camera models, so the same noise reduction slider value works well for a wide range of ISO’s. You don’t really need to set ISO-specific defaults now,
but if you do want to, there are a couple of options: The easy option is to use Jeffrey’s Bulk Settings plug-in after import. It allows you to apply noise-related
develop settings automatically to the selected photos, based on the camera/ ISO combination. Jeffrey’s plug-in can be downloaded from
http://regex.info/blog/lightroom-goodies/bulk-develop The other option is edit a Develop preset in a text editor to create an ISO-dependent preset, and assign the preset as a default."