Well, using that flag is risky. Flags are experimental, and the reason it is crashing is because it is an experimental feature that might not even be included in Chromium after all, just like so many flags that were removed by Chromium team, so, never depend on Flags, should the be the first rule, especially if they are causing crashes.
About the crash, it might be an upstream bug, I reported a crashing last time with this flag, and it was a Chromium issue that had to be fixed by them, that was for creating tab groups In Private mode.
It was fixed, but now there is still issues with it, currently Nightly crashed when detaching a tabs group from an In Private window.
For example, I found this one https://bugs.chromium.org/p/chromium/issues/detail?id=1456432 and in one comment it says:
Alright - so there is a fix for this. However, it landed in M116 and was not able to be merged back to M115 or M114. For this reason, the crash will just have to exist until the stable browser version catches up. This means that the feature just might not be usable on this platform until then
You have to remember, if you are using Stable, you will be 2 months behind in updates and fixes compared to Nightly. So if the bug is a Brave bug, it will take longer than if it was a Chromium bug, because Nightly uses Beta Chromium builds, while Stable is usually similar to it.
Right now Nightly is in the 115 and Stable 114, sometimes they have the same major Chromium version.
In fact, Tab Groups save flag, seems to work better in 115, but still crashes the browser, and if it is an upstream bug still causing issues, who knows when it will be fixed completely.
In other words… don’t use it, if you want to use it, well, that’s your risk and you should understand the message in the flags page that says they are
EXPERIMENTAL, and if they crash the browser, they will get eventually fixed or removed, but there is not priority about it, especially if the issue comes from Chromium.
Instead, you can use an extension like this:
Which has more useful features than just saving group tabs, if you want to use them like auto-grouping.