Yes, Anbox is working pretty well on Arch Linux ARM [0][1], although I haven't tried Signal specifically.

[0] https://github.com/dreemurrs-embedded/Pine64-Arch/releases

[1] https://github.com/dreemurrs-embedded/Pine64-Arch/wiki/Anbox

Anbox is so RAM-heavy that it really isn't a realistic solution for running Signal (or OSMAnd, another app that I need on my daily driver), at least not on the 2GB Pinephone board. Yes, Anbox support is moving right along so that you can open an Android app on your Pinephone, but not in a way that you can also use e.g. the web browser at the same time.

Ah, fair, I think I've only ever used it on a 3GB board with ZRAM enabled. It also looks a bit blurry on Wayland, hopefully that gets fixed soon (it looks like there's a bounty for it [0]).

[0] https://github.com/anbox/anbox/issues/1270

It can work, but it's definitely no fun to use it without ZRAM and/or swap (and better not wear your eMMC out by swapping to it).

I had no luck getting Signal for Android working in Anbox (too crashy). There are unofficial ports of Signal Desktop to aarch64 available here and there online, and there's also someone who got some sort of unholy Signal-Matrix hybrid working (https://old.reddit.com/r/PINE64official/comments/jusbk3/upda...) but the whole Signal situation is very much a work in progress.

Don’t forget about Axolotl: https://wiki.mobian-project.org/doku.php?id=axolotl