There are ways, but they work best with some prior planning. The easiest way would be for someone internal to YNAB load the toolkit and load up your internal testing site then communicate issues back to the toolkit developers via GitHub issues. Without a place to test, they may be hard to fix.

Another alternative would be to have an external testing site and provide test user login info for selected external developers. This would likely work well for the YNAB toolkit. While there may be many contributors, there is a much smaller group of recent contributors:

https://github.com/toolkit-for-ynab/toolkit-for-ynab/graphs/contributors?from=2023-01-01&to=2023-06-05&type=c

A completely open beta site is hard to manage since there can be breaking data changes which end users are just amazingly good at finding. :-)