Down Convert Creative Cloud Products 2020 to 2018

We had 10 CC 2020 and 6 Captivate licenses which expired last month.  Due to federal acquisition rules, we could not extend the licenses and were forced to the only approved version, CC 2018.  Our users advised there wouldn't be any compatibility problems, and now that we began installing CC 2018, it turns out nothing is compatible.

Regardless of the advice, we quickly need a path forward.  Help, please.