Currently we do not have any news from the development team about additional browser support for Vivaldi or Brave to share. Once we do have an update or add support for additional browsers we will be sure to note this on the Release Notes page as well.
I also want to upvote this feature request. Vivaldi has an open feature request as well. Please sort this out or I might need to try a different password manager that can support this browser. Appreciate all the hardwork and the great services you provide!
Another Vivaldi user here, waiting for LastPass update that will work correctly with Vivaldi Browser on Android. Actually I also started thinking about switching to different password manager, because how useful is password manager when it doesn't work with the browser of my choice? Especially when the fix is supposed to be pretty easy (as we saw with BitWarden as mentioned earlier).
You don't need to "officially support" another browser. Just make it work, please.
I find it quite annoying that this non-answer was marked as an "accepted solution" outside my control.
As has been pointed out by many people here, the problem seems to be that LastPass treats Vivaldi as an app (i.e. associates all websites to the same domain) instead of using the actual URL of the current website.
With Vivaldi being Chromium-based and the Vivaldi devs actively trying to work with LastPass to make this work, I can't imagine this being terribly complicated to resolve.
This thread is 10 months old, which is hardly grounds for optimism. Even if you're generously willing to grant LogMeIn the benefit of the doubt, be aware that the same issue still isn't fixed for Brave Beta, and LMI have had years already to remedy this.
The inescapable reality is that LMI are not driven to support browsers with a relatively tiny market share. You can debate the relative business merits of this stance, but that it is the company's (de facto) stance seems undeniable at this stage.
In fact, if you look at LastPass over the last couple of years, it's hard to reach a conclusion other than that LastPass development (on Android, at least) has stagnated and bitrot has set in. This is observable in the number of instances of LastPass mysteriously failing to fill log-in fields on Android having risen dramatically, to the point that the tool performing its core duties correctly is now a rather hit-or-miss affair.
All of which caused me to do a thorough re-evaluation of all of the current solutions available towards the end of last year and reach the lamentable conclusion that LastPass was no longer the best option for my family's set of requirements.
After a thorough and successful trial of Bitwarden, I have moved all of our family's data to that platform and haven't looked back. It has proven vastly more reliable than LastPass on Android, Windows and Linux, and has some very nice features, such as built-in TOTP generation for 2FA (so no separate app like LastPass Authenticator or Authy required any more) and regular expression matching.
Conversely, I have found only one useful feature in LastPass that is missing from Bitwarden, namely the ability to force re-entry of the master password for extremely sensitive sites. This is on Bitwarden's to-do list.
I certainly couldn't make the claim that Bitwarden is the best solution for anyone else, because that depends entirely on your particular requirements, but I can state with a high degree of confidence that you should be re-evaluating the current field of password management solutions and not relying on LMI to make a move. They have had ample time to remedy this and other issues already.
LastPass is observably yielding diminishing returns over time.