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once you are in the groups tap your profile pic and go to my account
head to security and you can change your encryption key password
personally i prefer memorable passphrases
if you forget/lose it you can still access your group settings and reset the key anytime you want
so
what this means is if you are only visiting public groups you don't have to input your key PW
to view private msgs you do have to input the key
also
each group you create you can set to have it's own PW tap the wee i for group settings top right < if you do this each person will need this PW to enter and join that group < this is separate from your E2E key PW
the E2E key is only for private msgs NOT public