when you redirect to slack to Create app from manifest and then you click YAML it will block you on an error (see screenshot)
From https://codercom.slack.com/archives/CJURPL8DN/p1760727979565079?thread_ts=1760674827.408439&cid=CJURPL8DN
This doesn't seem to block a user from creating a Slack app - need to investigate what the actual problem is.