Maybe the thing to do here, when web sites start enforcing this, is to swamp them with support requests. Don't write a screed or manifesto with ethical or technical reasons why this is wrong. Pretend to be a non-technically-inclined user and tell them you've spent hours trying to get it to work and your browser keeps throwing up errors you don't understand. They will ignore the principles, but if they think the technology is "too hard" for their "dumb users," that might carry more weight.
I don't think this will work. If companies can get away of slapping us by doing "please use Google Chrome or other Chromium-based browsers" just because Google implements the most niche, probably privacy-last, feature ever, then they will get away with it this time, again.
I literally can't log into the Amtrak Android app unless I have Chrome installed. It strictly relies on Chrome custom tabs. Other browsers that support custom tabs don't work.
I cannot imagine any reason for this except sheer ineptitude.
Guess what Amtrak support told me when I reported this as a bug?
As an AI language model, I cannot understand why you would not already have chrome installed. Chrome is a popular browser choice for the android operating system. Please check the app store for chrome.