“When you use Signal, your data is stored in encrypted form on your devices. The only information that is stored on the Signal servers for each account is the phone number you registered with, the date and time you joined the service, and the date you last logged on.”
If you have android, Molly is great 3rd party client.
I’ve tried it, it’s definitely better. If I absolutely had to use Signal I’d use it through a Matrix bridge.