I think during the edit of any step there should be a "Run Now" button.
The run should show a small popup to select the environment (and remember it) and then it should just run the step as is on the screen in that moment.

The results of the run should appear inline (or on a side bar) so I can edit/change the step and click again on "Run Now".
ATM to test a step during create/edit requires a lot of ceremony: Save Step, Create Release, Deploy Release, Select Environment, Click Advanced, Skip all other steps, click Deploy, review the error message then go back to edit my step.
This is especially painful when doing powershell on behalf of some azure Subscription.

Allowing a simply/super quick run would save hours of ceremony and clicks and allow me to quickly test any changes that I have.

Behind the scenes the whole process could be the process above, done automatically. It just does not need to be driven by me clicking around and waiting for screens to load.

This task https://octopusdeploy.uservoice.com/forums/170787-general/suggestions/3523937-run-arbitrary-powershell-scripts-on-the-tentacles unfortunately does not cut it as it can't run PS on behalf of an Azure account.

Implementing a Run Now would also partially maybe fix the Dry Run proposal https://octopusdeploy.uservoice.com/forums/170787-general/suggestions/6169634--dry-run-deployment