They've already added 5G to the SE and raised the price along with it.
If they've cancelled a 2024 refresh of the SE (which is still pretty far out), I bet this has something to do with the switch to USB-C. Apple is going to introduce the iPhone 15 line with USB-C next year, but they aren't going to run around and redesign all of their old iPhones that they still sell to include USB-C. That also rules out reusing an old product design for an updated SE (which they are so found of doing). By 2024, any SE would have to be an entire new design with USB-C...something Apple has proven unwillingly to do for a low cost iPhone. It may well be that the SE we have today will remain until a USB-C iPhone trickles down to the SE.