That’s good to know.

To save battery life I suppose. Also some phones may kill a background app even when told not to thus preventing messages from being received.

Probably something that does not require a phone number while still using google firebase notification system? Basically a less buggy version of session messenger.

From my understanding briar requires both clients to be online at the same time to use?

But do you use the equivalent of a Nokia 3210 phone?

Voyager is currently many versions ahead of the one listed on F-Droid. It is still usable but you may want to get the latest version from GitHub.

Use a phone with no Sim card and just connect to a WiFi hotspot when you need internet?

Well the base model of the perodua axia sold in Malaysia probably fits your requirements as it does not come with central locking or even a radio.