Pettern seems to be correct.
MS upgraded my X64 Windows 10 Enterprise N to Version 10.0.19041 Build 19041 last night, and this morning Vivaldi went to the pale V splash screen and then disappeared without trace. Several times.
So then I upgraded Vivaldi to the latest version , and as egigoka put it so well:
Steps:
Install Vivaldi 3.1+
Try to open
Expected behavior: browser opens
Experienced behavior: opens windows with Vivaldi logo and no interface for couple of seconds and closes...
After searching for a while here, I realised that it HAD to relate to something of MS's upgrade, and went looking there (Technet) , to discover that Win 10 N versions do not include the Media Feature Pack; it has to be installed separately.
So I did, and Vivaldi is back! Thank you all.
Posting this in the hope that it will help others to a speedier resolution...
Note that other than installing the latest version, I have done nothing to Vivaldi itself.
currently
Vivaldi 3.1.1929.45 (Stable channel) (64-bit)
Revision 1eb3263017ed42270818939fbff241845938a81f
OS Windows 10 OS Version 2004 (Build 19041.388)
JavaScript V8 8.3.110.13