Signal also requires you surrender to the Android/iOS duopoly to install the app on a device with a SIM to create that account. You can’t create an account on a SIM-less tablet; you can’t have a Linux phone. I’m not entirely sure if it behaves like LINE tho, where they will check in to see if the phone is still activated else it will kill access to your account from other platform--I have to keep Signal installed to talk to my family currently.