Browsers will never have a higher requirement. It’s the particular websites that will use newer technologies that older browsers may not support.

It may not be a mainline browser, but there’s no reason you couldn’t grab a new browser made to allow your currently out of date phone to use newer features, or at least the features your phone supported at launch. A cursory search on fdroid showed at least 1 browser with a requirement of android 4.4+.

The main thing to remember is that every website doesn’t take more power or newer technologies than the last. It’s only very specific situations where anything will need more power than something had 5 years ago. 99% of my apps could run on anything probably just fine. Email, Music, Audiobooks, VPN, 2FA etc. Most of those probably have security checks requiring a minimum OS version. Meaning they would actually work for longer on a phone with longterm OS updates than a phone that’s much stronger.

With the obvious exception being games. But I would never recommend thinking long term about games in any circumstance.