If needed, there is a way to enable Kerberos authentication in Vivaldi browser, the most working way is do it over registry:

 Windows Registry Editor Version 5.00

 [HKEY_CURRENT_USER\Software\Policies\Vivaldi]
 "AuthServerAllowlist"="*.domain.xxx"
 "AuthNegotiateDelegateAllowlist"="*.domain.xxx"

Tested and working.