I've recently finished a browser game specifically targeting an old iPad Air 1 we had lying around the house.
I had a working version after a weekend, but it took me a month to make it run smoothly on an over 10 years old mobile device. And the most recent browser available is almost 10 years old.
Surprisingly I didn't missed too many "modern" JS features, as these were mostly functional programming oriented which doesn't play well with optimization anyways, and the ES6 was more than enough as a programming platform.
Anyway, what I'm trying to say is that "the best practice" should be making your apps fast and accessible - as much as you can without having to sacrifice something you value - instead of chasing the latest and shiniest.
Don't be a fashion driven developer. :)