Or can I get a 2025 license and then run 2022 in a VM (will I need a key for that anyway?)?
For Windows Server Standard, you can have up to 2 VMs, or one host (for physical non-Hyper V roles) and one VM. In terms of downgrades, it depends upon the type of licence. For the sake of simplicity, I'm going to assume you don't have any kind of commercial agreement.
If you're buying a Reseller Option Kit (ROK) for an OEM-built server (e.g. licencing a prebuilt HP server) then you can ask the OEM (e.g. HP) for a downgrade key. In some cases, they provide a downgrade key for the most immediate prior version in the cardboard-backed, shrink-wrapped thin bundle of paperwork they supply with the assumption you may need it. For any older versions beyond that, you have to call the OEM to have those sent to you. These licences tend to be cheaper than full retail licences, but must correspond to the OEM providing the server hardware (e.g. HP ROK can't be used to licence a Dell server).
If it's a retail package (what Microsoft calls "FPP" or Full Packaged Product) in a box and it doesn't advertise having any kind of downgrade rights, then it might not have any at all. This is the version you'll need if you want to put Windows Server on any old hardware that wasn't from a specific server OEM. It's worth calling Microsoft to ask ahead of time and seeing if you can get an answer in writing just to be on the safe side when it comes to retail licences.
I've called them before and found with one particular retail licence (IIRC for Datacenter) that it did allow for downgrading to "any supported version" (so any non-EOL version at time of purchase) but the catch was that it still wouldn't actually come with any keys for the older versions. However, the generic AVMA keys would still activate any old Hyper-V VMs necessary for my use case at the time.
I hope this helps at least a tiny bit.
