I have been looking around to find out when the new "Data Explorer" charts will be mandatory in SaaS. Where can I get this information please.
The Data Explorer is still an early adopter. I cannot tell you if the "old" custom chart will be removed, but certainly, in a not so distant future, the data explorer will likely become the default.
Data Explorer is more powerful, but there are still features available in the old custom chart that the Explorer does not have yet.