I haven’t done curved 3D text, or seen tutorial on how to do it, but I might have an idea. Does it display a “CANNOT MODIFY BUILT-IN ENGINE ASSET” error?
If so, the way I solved this issue as @ClockworkOcean suggested is to not modify items directly from the Engine content folder (Fixed it using shapes from Modeling mode).
If that’s not the issue, you should start a new topic with more details about your issue as it is a bit out of this topic’s scope (Is it part of UE5 or a separate addon/Plugin? Does it show a pop-up error, if so what does it say? etc. etc.).
Sorry if I couldn’t help further. Best of luck on your troubleshooting.