The date/time picker code has not changed from previous versions of webwork. Furthermore, there is no javascript usage that should be a problem for any modern browser. So everything should work fine on Vivaldi and Opera.
WeBWorK Main Forum
date time picker is missing after upgrading to 2.16
This forum has a limit to the number of forum postings you can make in a given time period - this is currently set at 10 posting(s) in 1 day