Theres Beeper which I bought like a one year subscription back when it wasn't free and honestly its very useful and nice. I linked Whatsapp, iMessage, Signal, IG and discord and while in some cases it doesn't offer the same features it gets the essentials down and its really nice. Theres also another not open source one called texts.com or sth now which looks enticing but im gonna stay with beeper since I like the matrix protocol