As the others have said, with tanking having been simplified in the way that it has, there is only so much you can learn through Trusts I imagine. Absolutely go ahead and use it to establish a bit of experience and familiarise yourself with a particular dungeon and the damage you take at certain points. But with Trusts, you don't really need to be conscious of the convenience of other players, such as allowing them enough room to comfortably use their positional attacks in the case of AoEs nor with giving them appropriate space by repositioning the boss for upcoming mechanics and the like.

Also, if you plan on tanking with randoms at some point in the future then you need to be prepared for the likelihood of eventually coming across rude, impatient or outright obnoxious teammates, especially if you don't see yourself doing large pulls in later dungeons. I have honestly experienced very little of this myself in all the time I have been tanking but it does happen, to some more than others, so if you're okay with dealing with that after you have found your comfort zone then I'm sure you'll do just fine and get a good grasp of the fundamentals from Trusts.


On a side note, if you don't have a FC or friends with whom you can practice when you decide to give dungeons a try with actual people then I could maybe tag along for any of those if you think it would help you feel a bit more at ease. I'm pretty quiet and keep to myself in-game for the most part but if I happen to be around then it should be no trouble.