The fun part in web dev is to make sure everything works on the 0.5% non mainstream browser/platforms. Only supporting 99.5% is boring.

A popup "your OS browser combination is not supported, some things may not work" is a much less nuclear option.

If you know which parts will not work in advance. What if the "Send $$$" button does not appear due to a CSS misfire?

eslint-plugin-compat [0] and stylelint-no-unsupported-browser-features [1] can help you know when you're using an unsupported browser feature.