... *for me to better track myself in a way smart watches are as of yet unable to do so
As noted, this particular infinitive clause is ungrammatical with so. It's OK without so, however:
- ... for me to better track myself in a way smart watches are as of yet unable to do
and even better without do:
- ... for me to better track myself in a way smart watches are as of yet unable to
The reason for this is that do so represents some deleted verb phrase, as in
- Bill nodded and I did so, too.
where it represents nodded.
But in the original example sentence, the phrase unable to do is the remains of unable to track myself in
Some Particular way, and do so is not allowed with that kind of construction. Do by itself, on the other hand, is allowed after unable to, but it's optional, and the infinitive to by itself is enough.
Though being grammatical doesn't make this sentence any better. It's a terrible sentence, written (nobody would ever say this sentence) by someone who thought that importance and clarity was a matter of big words and plenty of them, in complex constructions and as many subordinate clauses and connotations as possbible.
As of yet is consciously archaic; say so far. The better serves no purpose.
In a way should be the way.
- ... for me to track myself the way smart watches are so far unable to
or, shifting the negative to a more prominent position
- ... for me to track myself the way no smart watch is able to so far