Requiring a phone number is literally my only complaint about Signal, I used to just use a Google Voice number but then I learned about TextNow and have been migrating away from Google as much as possible
It seems unlikely that big tech and telecom corporations, whose lifeblood is personal data harvesting, or government, with surveillance states becoming the global norm, are going to agree to adopt a genuinely secure end to end encrypted messaging standard or protocol on the best devices ever to facilitate their practices.