I installed Qubes 4.3 on a new laptop with the default 6.18.x Dom0 kernel. I regularly update Dom0 but I am still stuck on 6.18.x. I have tried the latest repository but I am still on 6.18.x.
You need to install kernel-latest in dom0. Unless your current hardware is not working properly, I see no reason to upgrade, since security patches are backported.