KiCad has not used the old RS-274-D for many years as far as I know.
KiCad uses the RS-274-X2 by default, and if there are problems with gerber files for PCB manufacturers, it usually is because they use the older RS274-X1 format.
Why do you think KiCad uses the older format? Did you get a complaint from a PCB manufacturer? It might help if you turn of the extended X2 attributes in: Pcbnew / File / Plot / Gerber Options / [ ] Use extended X2 format
I’m not entirely sure, but I think this checkbox switches between the newer RS-274-X2 and the older RS-274-X1 format, and the old RS-274-D is not used at all. It has been obsolete for quite some years now.
A big part of the problems with Gerber files are because manufacturers use old formats, because they need something that works with their old machines, which are expensive to replace, and difficult to update. It is (unfortunately) relatively common that manufacturers have to write their own (sometimes bodged) software to translate incoming files to something their machines understand.
It’s a bit of a struggle. Manufacturers can not update because their hardware is expensive, and still works. KiCad can not implement all the newest features because many manufacturers use older hard and software.