You can mount it, so can you tame it?
While it seems there are a multitude of secret mounts (non-horses of any kind) that you can mount and ride around, they are not mounts that you can register/keep, while you are able to tame/ride them.
This article talks about all the different mounts and explains based on player's accounts that unique mounts such as bears are only able to be mounted, and as soon as you get off, they will walk off too. I won't post more from there as some mounts could be potentially seen as spoilers.
Horses aren’t the only animals that can be tamed – we’ve seen a player riding an elk in one video. The taming process is the same as with horses, but there are some key differences. You can’t register wild mounts, which means they’ll be off as soon as you dismount them. They also have unique characteristics – they may be slower, but provide something else in return. We’ve seen one player mounting a bear. He said he couldn’t make the bear attack, but it did seem to scare a lot of the enemies away, so there’s that.
Update: It is impossible sadly... got him down to beaten n blodeied pulp but just alive... froze him n got ontop, another 30 rings of stamina and nope!. the reason it comes up mount is so you can jump on it's back n smack the shit out of it. Sorry guys... this bastard iv been after to have as my own for the last 2 days.
So, I've been dodging his attacks until hebtries his fire blast, then shoot it with an ice arrow. He falls to the ground and you can mount him pretty easy. Still can't take him, i assume.
As for what I found is you can fly on to the lynels and from there they are Easyer to tame if you freeze a horse and jump on its back it takes more stamina so I think the same applies to these lynels. I have not tested this but I think it’s a good theory I hope someone try’s it . Good luck 😄
Near to Seres Scablands there is a npc that tells of a story he heard about lynels which says you can ride them. So keep on trying ;)