Hello @frank46 and welcome to the NVIDIA developer forums!
The Desktop or rather workstation GPU RTX A4000 does indeed already support Resizable Bar.
How did you determine that it does not?
There are some preparation steps to get it to work on specific systems, but Hardware wise it is supported.
A good place to see all the details on the feature is actually the Geforce RTX 30 series page on the topic. Even if this is not directly about Quadro cards, the requirements section as well as the links to resources are applicable for those as well.
Let us know if this helps.
Thanks!