You may try understanding the word "*that*" in this way, with the assumption of an optional element dropped:

>  I also did not love *(the fact)* **that** for most purposes, the AirTag requires buying a separate accessory, ...

Now it's an *appositive subordinate clause*, where "*the fact*" and the whole subordinate clause beginning with "*that*" refer to the same thing.

In fact, there are many more possible replacement words that fit right there, for example:

- I like (it) that ...
- I like (the assumption) that ...
- I like (the implication) that ...

As long as the word in the parentheses matches that of the subordinate clause, you're good to go.