Hey @hkeric.wci! My computer crashed recently and I’m having to use Report Builder 2019 since that is the only download MS is offering. I had been on 3.0. Are you saying that once I open and save a report in 2019, then someone else opening it in version 3.0 will be unsuccessful?
Also, are there any tricks to connecting to the report server in 2019? Neither I or my IT person have been able to get connected 
I keep getting a HTTP status 401: unauthorized error.
-> edit: scratch that. ended up finding a download for 3.0 and connected now! 
guessing that has something to do with SQL Server 2012…?
Thanks for your help!