Google Messages have E2E encryption and support SMS, if other party doesn't have Chat feature, only comparable app is Signal, I used it for years until I gave up after nagging PIN popup, during this period I experienced extensive problems with sending/receiving problems if you often switch between mobile network and WiFi Signal is very slow to recognize this and choose the best network, while Whatsapp does this almost instantly

Signal has also pretty horrible management, I remember one day outage for many house because admins in US just went sleep, so Signal is all nice if you dont care about reliability and can get through bad UX, for instance very well hidden option for force sending SMS to Signal contact through long tap Send button, there is now ay to find this during using the app