Well, i think coreelec going to stop their support for the VIM3/3L and older khadas boards.
Im not a coreelec expert so…(im an android dev) the one still being updated and working on older khadas devices is LibreElec is almost same as coreelec diferent team(former coreelec devs…)
here is the link to their latest builds.
Now how to install, this is from correlec wiki but its same for libreelec:
https://wiki.coreelec.org/coreelec:khadas
Good luck.