How about a climbing gym? You're fighting gravity and losing. It spikes my adrenaline more than most hikes and works out the entire body.

Wear a helmet

You can do martial arts without free sparring. You can take stage combat class. Still some risk of betting bonked but much less. You could do foil fencing, idk if it's even possible to concuss someone with a foil. Same with shinai fencing, hard to concuss someone in a helmet with a bamboo stick. You could get a wooden or plastic sword and a shield, build a pell (training dummy) and practice on that. You could take up katana cutting, which is all about precise cutting and less sparring.you could check out hema and see how that feels. You could do archery. You could practice throwing knives until you get real good at it. You could take up airsoft. You could get a vr rig, there's lots of vr combat games. You could take up any kind of dance. Dance is like 70% of the way to martial arts.

I saw you didn't like fencing. You could check out medieval fencing with the sca or look in to boffer larps. Arrow tag is a thing in some lpaces.

Oh, if you have a vr rig there's a totally bonkers game called Rumble. It's earthbending: the vr game. It's athletic for a vr game and you need to be really on your game in comp play.

There's flag football. It really rewards good footwork and you probably won't smack your head.q

I present to you a solution:

Concussions are a conspiracy by big helmet. They used Tony hawk to get us to fall for their lies. /joke

Not finding a huge amount of consistency in the options you're considering OP. Is it the adrenaline and the heart pumping you're looking for? I suggest trying anything close and convenient and affordable to try out. I think all of these can go either the fun or tedious route depending on the day and other circumstances. Btw. You are highly unlikely to get concussed learning martial arts if you don't compete. Maybe exceptions for hyper-masculine MMA and thai kickboxing joints.

Bout the most predictable is VR which is pretty reliable but I cannot in good conscience suggest it to a comrade in lieu of literally any other physical and/or social activity. Actually VR fishing with friends is fucking cool.

Personally I like riding an electric skateboard. With leathers, pads and a helmet. a- actually, I look cool as fuck and not at all lame.

You're looking for BJJ lol. Its entire appeal is a martial art that doesn't require you to get hit in the head repeatedly. Wrestling for adults.

Go frogging

Certain kinds of paintball might be worth a try to get a feel for it. Most places are all about speedball because selling paintballs is a big part of the business model. Speedball is all about constant covering fire. I got bored of it eventually because it’s mostly about having 800+ ammo and a ridiculously high rate of fire. Then there’s brushball which is mostly stalking the woods in camo.

The closest I've gotten to that feeling with something that's a little less dangerous is kettlebell training. There's a martial arts feel to some of the unique bell movements, like the snatch or the high pull, where you move your body explosively, but with precise form. Olympic lifting kind of does this, but it has nothing on kettlebells imo. Moving 62 lbs of iron around your forearms as you sling it through the air feels so cool once you've mastered it. If you haven't tried them, I'd recommend it.

you know that 99% of martial arts is practicing the same punch 1000 times by yourself, not finding random dudes to throw punches with? There's lots of intense fighting things you can do with only a punching bag. The risk is basically zero unless you try to 1v1 somebody.

also slow mountain biking is awesome.

Bouldering and parkour.

collect fossils instead

bike on flat ground or one of them velodromes?

Martial arts are really fun and great exercise! They also do a really good job as a confidence boost towards other people.

I don't know if it's a thing or not, but I also notice that they tend to attract people with a sense of comradery, helping one another improve and work through mistakes.

Beat saber is pretty freaking fun. There's some decent VR boxing games out there too. I quite liked knockout league as it had some pretty cool training mini games.

Now I'm kinda miffed because I don't think I've hit that sweet spot myself since quitting competitive team based shooter games.

Fencing

As a former fencer I'm going to need to take a breather. That being said, depending on where you are you may be able to find sabre fencing. Pretty much everything in that is a legal shot, plus you got the nifty mask.

Another option is trail running. You can still run up and down ski hills like a mountain biker, but it might get you close to that rush without risking the more serious of injuries.

Fighting Games can be toxic but are pretty good too. Excuse all the random thoughts I'm just trying to figure out how I used to scratch this itch myself.