My experience with kernels on dom0 boils down to “If it ain’t broke, don’t fix it”.
Upgrading to the latest kernel tends to break things that were previously working. For example, suspension and hiberation works for my laptop with the current kernel, but gets completely broken with kernel-latest (5.6). However, on another laptop where the current kernel leads to the iGPU spitting out a slideshow instead of a functional desktop, upgrading to kernel-latest fixed the problem completely (while also killing suspension). If there isn’t any major issue that desperately needs to be fixed, I’d stick with the current 4.19.
I can’t seem to find it, but in one of my earliest threads in the mailing list, I asked whether there are significant security advantages to using the latest kernels in VMs–the answer was ‘No’. For dom0, I’d reason that the kernel will be the least of your problems if you’re facing an adversary that can get to your dom0 through a compromised Xen, but I’m not technical nor an expert on anything, so take what I say with a grain of salt.