Kate. Its such a brilliant foundation.
I currently have no idea of how to do it but in theory you can add any languages autocomplete, as well as huge libraries of auto-text (like in VSCode, templates for code stuff).
And its fast, unlike stupid electron VSCodium
I’m a new Kate convert. I had some issue on my system where GTK apps would break under Nvidia, something to do with font rendering. I tried Kate and was like “cool it works” and then I discovered how amazing and lightweight it is. Great editor.