Can I count solo complex time as complex training time for a commercial certificate? Does a combination of both dual and solo hours in a complex aircraft (PA28R-180) which total 10 or more flight hours meet the commercial pilot training requirements of FAR 61.129(a)(3)(ii) or must all the hours be dual instruction?
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.