@Mei :verified_flashing: Yeah. I managed to do it by hitting CTRL+SHIFT+T repeatedly until the window came back, and then laboriously closing the dozens of tabs I actually didn't want open.
Right now I'm in the processes of updating all my custom v2 extensions to v3, since I didn't realise this change was coming and had I, I wouldn't have accepted the latest browser update right away. v3 makes a bunch of things impossible and adds a lot of extra convolution to stuff which was extremely simple and straight forward to do with v2. If I had a bit of notice this was gonna happen though, I'd have already converted them. I thought Brave was gonna support v2 indefinitely, but I guess they finally caved or got forced into it due to architectural incompatibility.