I mean its two different things: Nokia a mega corp (at the time) and Pine64 (a few hardware enthusiasts + small overworked dev community).
I get your frustrations and as a PinePhone owner myself I would not consider it anywhere near usable as a real Smartphone replacement.
However after installing Arch it is pretty snappy and has certainly sparked some new hope in me. I really recommend you to check it out.
For Signal there is (or will be) Axolotl [-1] which looks promising and when it comes to developer support both KDE and GNOME devs show some support for it. E.g. GNOME recently announced libadwaita [0]. Give it some time and check out the Arch release for PinePhone: [1].
[-1]: https://github.com/nanu-c/axolotl
[0]: https://aplazas.pages.gitlab.gnome.org/blog/blog/2021/03/31/...