You may be able to get telegram working on a KaiOS flip phone, but those can actually access the internet as well (very shitty, has huge 2004 RAZR web browser energy). Signal does not and will not ever have a presence on KaiOS unless someone with very very deep pockets decides to throw absurd money at the signal maintainers with the specific demand that they create and maintain an official KaiOS store webapp because of the way that KaiOS works.

If you want to escape app hell, maybe try a Pine phone and run an open source OS on it. It probably won't stop you from accessing the internet, though.