@liggar reset all those flags to their default values, relaunch the browser, then check again and it should be fine. Additionally, it’s worth noting that the toggle may just appear gray because it’s not enabled – when you click it, it should still work and toggle “on”.
I have the exact same issue after setting up Brave anew. Did a reset to default for all flags and relaunched, but vertical tabs are still grayed out and cannot be turned on in the settings. Also, changing the settings from brave://flags does not help.
Using the latest version 1.92.134 with Mac OS 15.7.7.
Would much appraciate any help. On my previous device, I’ve been usign vertical tabs since it’s been released so it’s tough to go back.