Every developer had the opportunity to update their products to work with new major release of macOS. If Play Online opted not to do so or not do so at this time, there is really nothing Apple, nor anyone here, can assist you with to get this resolved.
You basically are left with three options:
- Wait until Play Online updates their product to work with macOS Catalina.
- Either downgrade your Mac to an earlier macOS release or use a VM manager, like Parallels or VMware, and use a VM of an earlier OS.
- Change your ISP.