Have to note that the current behavior actually STOPS the creation of new apps rather than kindly warns you.
Steps to replicate:
1. create a new pool (in my case, burner)
2. click custom app in the Apps top bar
3. create a new nginx container, map /mnt/burner -> /burner, keeps everything else as default.
4. modal pops up.
View attachment 73061
Thanks for your reminder of it is possible to attach the mapping later but the current behavior is misleading at least.
Hope there could be a 'I accept the risks and continue' toggle or something.