This isn’t very clear from most sources, but the consensus in this forum seems to be that population “average” treatment effect estimates aren’t exceptionally useful (especially the “standardized” mean difference), and odds ratios are a good default, as they have an interpretation for individuals.
Senn’s article U is for Unease (in the links above) goes into the issues about effect size measures and how they can increase or decrease heterogeneity.
If the variable of interest has natural units, an average treatment effect could make sense. For PRO, they don’t.
This thread also goes into the challenges of aggregating estimates from studies.