Remove the limitation entirely or allow the access/downloading of assets in libraries for platforms or engine versions that are not “supported” by them.
Most assets or textures that have an inactive publisher have unrealistic limitations that need not apply. Some publishers don’t add Mac for example, because they do not have access. While I should be aware of this during purchase, it should not prevent me from downloading it.
ie: a simple .obj or .fbx file should not be limited to just Windows on Unreal Engine 5.3, since they can be used on any OS and any Unreal Engine version.
If needed simply make them so that a message is displayed with confirmation box “Do you acknowledge this product requires the use of …” and allow the download anyways.
Requiring the setup of another OS and engine version is unnecessary in almost all cases.