Can't figure this out. My daughter and I both have S20 FE and there's a strange problem when we send each other text messages. If one of us sends a text to the other but happens to be online at the time then the message won't be received until the other one has turned on WiFi or data. Now I know texts should have nothing to do with Internet access so I'm totally confused. Is there an option on Samsung phones that operates like imessaging on iPhone? Please help. Thanks.
Sounds like you've got chat features enabled (which works over WiFi or data rather than SMS service).
If you go to Messages app -> 3 dots at top right -> Settings -> Chat Settings. Toggle off chat features option. Further down settings also change default message type to 'Text or multimedia' Handset will then only use networks SMS service for messages.