The app supports 64bit!! It seems you downloaded the apk for 32bit platform, if you are using IzzyOnDroid repo, that only provides the 32bit apk, switch to the official F-Droid repo, install from Google Play or download the apk for 64bit manually from the github releases page
There are a lot of reasons for each of those will try to provide some at a glance:
SimpleX, XMPP, Matrix: The client is more user friendly, less buggy and less “this is for nerds” UI than the clients of those networks, ArcaneChat is more on the WhatsApp-like UI
Signal is centralized, depends on phone numbers so can’t be used by children in the family that don’t have access to SIM card yet etc. Registering in Signal is also more complicated, SMS verification, solving captcha etc. No good multi-account and multi-device as ArcaneChat.
Groups in ArcaneChat are managed independent of the server while in XMPP they are created on a given server and if the server dies the group is lost, while in matrix a lot of group state is replicated and tracked by the servers, in XMPP is easy to end up with unencrypted groups and in Matrix you often get “unable to decrypt” and emoji reaction are not even encrypted, ArcaneChat groups are always encrypted and safe against MITM (green checkmark displayed in the group name)
ArcaneChat has in-chat mini-apps that work independent of any server, communication is only between chat members and e2e encrypted, for example collaborative editor in chat, shopping list, split bill app, several mini games with shared scoreboards etc.
ArcaneChat works offline-first unlike many(all?) of the previous mentioned apps you can even create groups while being offline use and modify the in-chat apps and all state will be synchronized when you are back online. The app also works in slow and unstable connectivity when most of the other mentioned apps would simply not manage to connect.
I wrote to the admin asking for including the 64bit version, let’s see