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Hi there!
We have added a Linux application bundle (included in an .sh file) in ScreenConnect version 23.5. However, we didn't remove the ability to use the .jnlp. there should still be a fallback join mode 'WebStartDirect' that should allow joining a session with the .jnlp (it would require a 3rd Party Plugin called IcedTea to run though)

If you are still having issues after checking this, please contact our support team for assistance.

Contact Support (site.com)

This has been released with version 2023.5:

ScreenConnect 2023.5 Release notes - ConnectWise

(I know those notes are from the Preview release, but as of yesterday we have begun rolling out the updates to our cloud instances)

We are currently implementing some of the required services to support this. We started a bit later than initially planned, but I am hoping we will have something beta ready by mid-August.

Please reach out to our support team for assistance as they are best equipped to troubleshoot this issue you are facing.
Contact Support (site.com)

We currently have development scheduled to begin work on this in early June so likely looking at late June (at the earliest) for first beta build. 

Thanks for the feedback! We are always evaluating the feature/package balance, and as of now it is not available in either Free or One packages.