Can I count solo complex time as complex training time for a commercial certificate?
As you already noted, 61.129(a)(3)(ii) says &quot;training&quot; (emphasis mine):

(ii) 10 hours of training in a complex airplane, a turbine-powered
airplane, or a technically advanced airplane (TAA) that meets the
requirements of paragraph (j) of this section, or any combination
thereof. [...]

Here's the definition of training in part 61, per 14 CFR 61.1:

Training time means training received—
(i) In flight from an authorized instructor;
(ii) On the ground from an authorized instructor; or
(iii) In a flight simulator or flight training device from an
authorized instructor.

According to that definition training always requires an instructor so there's no way you could log solo time as training time. All 10 hours must be dual instruction.