There are limitations concerning the number of versions and aliases of app bundles and activities you can have:
https://forge.autodesk.com/en/docs/design-automation/v3/developers_guide/rate-limits/da-rate-limits/
At the time of writing this article the limit for both versions and aliases are 100 for all Design Automation services:
The easiest way to delete your oldest versions and aliases on a one-off basis is to use a utility like https://da-manager.autodesk.io/ or the Forge Visual Studio Code extension.
Once you did that you should be able to create new versions and aliases again.