Signal allows you to do local chat export for backup, as opposed to WhatsApp (which only allows backup to Google account on android). That's actually my biggest complaint against WhatsApp and Viber: why don't you allow local backup, or backup to something I control?
Correction, in case you're interested: Whatsapp does (and has always done) allow local file backups. I know because they are just there on the storage:
Android/media/com.whatsapp/WhatsApp/Backups/
I also know because for many years I was VERY cloud-averse so for several iterations of smartphone purchases I did migrate my chat backups between phones (plain copy-paste of files with a computer) without issues.
