Mainline (formerly ukuu) and/or HWE to update Ubuntu kernel

Has anyone here tried and was successful in using HWE or mainline to update the kernel to 5.x in rock960’s official Ubuntu image?

When using either HWE (apt install linux-generic-hwe-18.04) or the compiled mainline I see the following errors: Warning: root device does not exist, cp: cannot stat '/usr/lib/linux-image-5.X.Y-xxxxxx-generic: No such file or directory' and
package post-installation script subprocess returned error exit status 1 Errors were encountered while processing: linux-image-unsigned-5.X.Y-xxxxxx-generic E: Installation completed with errors

I can coerce the installer to resolve quietly by symlinking the 4.4 version of linux-image from /usr/lib/ or by supplying a crosscompiled dtbs folder at /usr/lib/linux-image-5.X.Y-xxxxxx-generic but there is no joy in the end. Tried with 5.4.0 and 5.11.5, still stuck with Ubuntu running 4.4.