For Signal I just did it (CalyOS FP4 to my interims Phone FP3 DivestOS).
Works as described (my Signal container is 12GB btw.). But I also had the normal local backup at hand in case of issues. It took me 2 attempts to establish the Direct-WIFI between the devices but afterwards it went fine.
I though I made some screenshots, but I probably deleted them already again, but it is quite good described:
Just follow the Transfer from Android device variant. It creates a Wifi between the 2 devices and transfers the account including all messages (media stuff etc.). Final step is activating the Signal Account on the new phone, on the old one it is disabled then. Cannot be active on 2 phones (like Telegram or so)
WA to be tested (I don’t use it personally), but described here and sounds similar: https://faq.whatsapp.com/209942271778103/?cms_platform=android
Edit:
Ah found the pictures I took with the other devices and vice-versa
Source Phone (“old” Phone)
Target Phone (New Phone)
