The only way is by being big enough to be worth their time

Make PWA's the go to. Use them where possible and give feedback where possible

@Beaver
I don't think we need to entice them. The only reason bank apps are necessary is because they don't use standard 2FA.
What we need is to get legislators like the @EU_Commission to force them to follow standards (so we can use our own 2FA apps or keys, that have been working just fine for decades and are way more secure than some of their "2FA" implementations) and make their websites usable on a mobile browser.

I really want to have the proton email client with 2FA key support on Linux phone distros.

I'm feeling like the place to start is by requesting the support from companies.