Phones that run neither Android nor iOS have been falling behind in terms of their browser and web-based support. Mozilla and KaiOS (the mobile platform most likely to run on such devices) have addressed this through a new partnership by which the former will keep devices running the latter much more up to date in their ability to use the internet.
https://www.notebookcheck.net/Mozilla-and-KaiOS-new-partnership-may-result-in-a-better-future-for-feature-phones.457460.0.html