We have a solution , As a permanent fix, we will applied a hotfix. The deployment is in progress now. It'll take some time to roll out across all regions. Hopefully in next 24 hours it should be live.
Until it is done, the workaround should help in unblocking you. Please let me know if that helps.
A quick workaround for this can be achieved by taking the browser URL you land on in Copilot studio:
And then find the querystring parameter in the URL called $azureOpenAIResourceId.
A forward slash / needs to be prepended before "subscriptions".
So for the provided URL, you would turn $azureOpenAIResourceId=subscriptions into $azureOpenAIResourceId=/subscriptions