The data are freely available for academic use and other non-commercial use. Redistribution or commercial use is not allowed without prior permission.
Using the data to create maps for publishing of academic research articles is allowed. Thus you can use the maps you made with GADM data for figures in articles published by PLoS, Springer Nature, Elsevier, MDPI, etc. You are allowed (but not required) to publish these articles (and the maps they contain) under an open license such as CC-BY as is the case with PLoS journals and may be the case with other open access articles.
Data for the following countries is covered by a a different license
Austria: Creative Commons Attribution-ShareAlike 2.0 (source: Government of Ausria)