When using non-supported kernels; you take on the job of applying all security updates/fixes to the kernel yourself, which is no easy task if your box is online.
I’ve only used those to install kernels for testing purposes; where we’d contrast specific kernels with the default supported kernels with regards a specific bug, then I’d uninstall the packages; I’ve not tried to live with it & manually support, nor have I used if often enough to feel confident to support others.
I really and highly appreciate your detailed explanation, which helps me to understand the situation and make the decision. I will wait for that software to support the kernel 5.13.