True strike is also a concentration spell, which means you can’t use any other concentration spells and you have a chance to waste it if someone hits you.
It’s also “advantage on one attack roll”, meaning it has no effect on spell saving throws like Fireball, Ray of Frost, etc.
There’s just a huge opportunity cost of taking it when you only get a few cantrips for the whole game
Also action economy it’s stupid. You use one action to apply it so on the next round you can use two dice. But if you had just attacked instead you would have already done two attack rolls. And frankly there’s better ways to gain advantage. Many if not most of those better ways apply to multiple characters attacks instead of just yours.
Everything has a huge opportunity cost. You’re giving up alternatives for every choice you make. Lowering variance of high impact attacks has value if you choose to play that way. Missing can turn a battle.
It doesn’t have to be useful to every choice of every build to have its existence justified. There are plenty of choices of spells, equipment, etc that I can look at and tell you “I’ll play 20 different times 20 different ways and never be tempted to use that once”. That’s perfectly fine.
I’m not saying “True Strike shouldn’t exist”. I’m saying as it is, it’s incredibly underbalanced and not worth spending two turns to cast one spell.
I’m all for build diversity, but if you want to guarantee your big spells land (you can still miss with advantage, btw) you might as well pick Divination Wizard and use a Portent. If someone wanted to use this cantrip and I was DMing, I’d adjust it to be more accessible.