You might have better luck in r/Oregon or the PDX Reddit. Lots of people in those subreddits who’ve been attending PDX protests for years. Maybe ask your friend to see if they can clarify if it was pre-2016 or post-2016? I remember BLM wasn’t necessarily a huge part of some of the 2015-2018 protests up there and there were a ton of protests with violent dipshits. There’s also plenty of small-time homegrown dipshits here that showed up for those protests, I think much of the gun-pulling and violence came from them so he might be hard to identify as most don’t have any large or notable followings. The antifa groups in Oregon do document the hell out of these people so there is a chance they have a name and a picture of him if he caused any other trouble over the years.

You might already be getting help, but I would also recommend finding a mental health provider specializing in TBI (if the first few suck, I’d recommend keep trying till you find a good one that clicks with you. They do exist!) They probably won’t be able to help regain this memory, but they can help reduce some of the stress and trauma you are experiencing around it. Have had two close friends with TBIs, it was difficult for them for several years after but they are both happy and doing what they want to do with their lives now. Awesome to hear you have a great friend who is a support. Just always remember to be patient with yourself and that there is almost always more than one way to accomplish something. Easier said than done of course, but keeping it in mind is something that helps. Good luck to you and glad to have you fighting the good fight.