Easiest and safest way to tame this is to lure it under water. They stop aggro and you can tame as you please. Just make sure you come up for air every once in a while. Also be sure the water is deep enough.
This is my attempt to bring together all the tips that worked for me and explain how things went for me playing on an official pve server on The Center map, and specifically the volcano cave. You can’t be mounted to get into the opening to the entrance tunnel of the cave, and then again at the end of the tunnel as you enter the actual cave. You can’t build in here, but you can place sleeping bags.
Don’t be lazy - make broth of enlightenment. Kill woolly rhinos for their horns and the broth is easy. Your entire goal during taming is to minimize the number of contacts with the arthro. During the winter event in 2022 with 3x taming, a single broth of enlightenment will tame a 150 arthro. My advice: make and bring more than one broth - the chances of encountering multiple high levels worth taming are pretty high. You may as well make the trip worthwhile.
Next, Don’t be lazy - have plenty of bug repellent and the best set of ghillie you can get together. I go ahead and use both during the whole trip (except a max armor ascendant flak helmet), because bug repellent doesn’t work on titanboas, etc., that are likely to be present in the same places as the arthros. Plan for disaster and come prepared for that.
It is absolutely true that theris do not aggro the cave dinos **while you are riding it** so bring one if you’ve got it. Just remember that once you dismount, things can change in a hurry, especially if you aren’t using bug repellent and ghillie, or if you just didn’t see a boa or something. By comparison, a shadowmane aggros everything. Personally, I bring a few standards with me in cryos, including a theri and a megatherium. If push comes to shove and you have to start killing everything that moves, you are literally in the megatherium’s wheelhouse. It’ll be enraged the entire time (and slot cap with chitin if you need it). I also bring a shadowmane for the water, but you’ll be fine without it.
The arthros won’t aggro while your theri kills other stuff right by it (except another arthro), just as long as nothing hits the arthro. So try to clear everything else that is anywhere close to your arthro without hitting it. One time there were two arthros right next to each other, one a 150 and the other a 55, and I couldn’t kill the 55 without drawing aggro from the 150. So I tamed the 150, and the 55 immediately aggro’d the now tamed 224 arthro and then managed to hit me before the 224 killed it. But that bite hurts.
Finally, I suggest you have a plan for what you’ll do if you die in a big nasty snake and bug pile, where all your stuff will be. One time, there were so many araneo shooting webs that Ark crashed, and I was dead when I logged back in - my tame was alive because it was on neutral, but it fell off a ledge and definitely didn’t kill everything that was by my bag. I also couldn’t whistle it back from where it was to the closest sleeping bag I dropped. I was able to run to my tame naked since we had cleared that route, but it was sketchy and not what I would ever want to do again. From then on, I had a box with a bed and a mortar&pestle as close to the cave entrance as I could safely place it. Before going in the cave, I would leave a few things in the mortar&pestle to use if I died / like a megatherium and a flyer in cryos, extra bug repellent, armor/weapons, whatever else you’d want to have on the way back to your bag. Use th flyer to get back to the cave entrance, then ride the mega or whatever beast tame you bring until you get back to your bag. It maybe takes an extra couple minutes, but if you try to just spawn in on sleeping bags in the cave without any gear or tames waiting for you, there’s a good chance you’ll just end up getting killed over and over again as you struggle to get your stuff back.