I've downloaded it again and installed it. Still gets to the screen with the V, sits unmoving for 15 minutes, and shuts itself down. At least it's no longer crashing my whole computer this time.
I was curious to try this browser after reading about its "standalone" version that claims "The browser is self-contained within a single folder including all user data and, unless made available as a default app, won’t be added to the operating system’s registry."
I made a folder C:\Vivaldi to hold the install and began the process after downloading the latest 5.7 x64 version. As per the web help, I specified "Install standalone", changed the install path to the folder I just made, definitely UN-checked "Make standalone available as a default app," and checked "Disable automatic updates."
After choosing to continue the install, it seemed to proceed normally, and finally brought up the browser full-screen with the option to select 1 of 3 general setup packages--I left it on the "normal" default, and when attempting to hit the "proceed" (sic) button, nothing happened. Setup was frozen at this first screen, which could not be exited or changed and I had to kill with Task Manager. The same result when tried a second time.
Checking my install monitor (RegShot64) I found that despite expectations it had indeed made an entry in my registry, adding a key and sub-keys of setup information in HKCU/Software/Vivaldi.
At no time did Windows Defender or my Firewall policy react. While I suspect white-listing the new folder may have made a difference I am not anxious to try that considering the "sneaky" registry entry.
Windows 10 22h2 x64. Windows Defender only for anti-malware/virus. This just posted as a one-off FYI for others, won't bother registering for a Vivaldi user forum when I haven't been able to USE it yet