There are some lists maintained for different purposes.
The machines in the Certified hardware | Qubes OS are officially supported & tested, and can be purchased with QubesOS pre-installed.
The Hardware compatibility list (HCL) | Qubes OS contains a larger number of machines with compatibility details based on community-submitted results. Not all of these are 100% compatible, but you can see which parts are incompatible and maybe you’re OK with the compromise.
The forum also has a community-maintained list of recommendations (Community-recommended computers), which are not officially supported but have been found to work with minimal difficulty by experience.
Personally, I use a Librem 14 by Purism; I’ve run into no significant difficulties and appreciate the design of PureBoot. It’s not a certified machine but it can be purchased with QubesOS pre-installed. I’d be wary of some of the other products though. For example, the Librem Mini claims to support PureBoot but it does not have a TPM, so it is not clear to me how this protects from the threats that PureBoot is designed to protect against (I assume a physical attacker could read the software and replace it with a malicious version that knows the secret because the secret is not protected by a TPM, but I have not looked at this in great detail).