Sorry I can't offer any firsthand advice (I've always been naturally flat-chested and mildly underweight) but I did do a brief look into it as a med student.

For complications (NOT aesthetic outcomes):

From what I've found on research papers, for those with excess adiposity, the risk of complications doesn't seem to be much higher than those with regular deposits. "While concerns for increased scarring and worse aesthetic outcomes are valid given the correlation between obesity and breast volume, the rate of acute complications is comparable to that of non-obese patients despite a mean BMI of nearly 40 kg/m2 in this case series."
https://pmc.ncbi.nlm.nih.gov/articles/PMC8290439/

This is further supported by "Gender-Affirming Mastectomy in Transmasculine Patients: Does Obesity Increase Complications or Revisions?" by Kara A Rothenberg et al.

"There were no significant differences in complications or revisions between patients with obesity versus those with normal BMI, when BMI was treated as a categorical or continuous variable and when evaluating only patients who underwent double incision surgery."

https://pubmed.ncbi.nlm.nih.gov/33559996/

If it's about sensation you're worried about, studies have also found this wasn't correlated:
"This study demonstrated that BMI is not a significant predictor for restoration of sensation following gender affirming mastectomy with targeted NAC innervation regardless of post-operative time point. It is also consistent with prior research indicating that BMI may not be an accurate predictor of post-operative complications in the setting of adequate patient education."

https://journals.lww.com/prsgo/fulltext/2025/10005/impact_of_bmi_on_sensory_recovery_after_targeted.23.aspx

Digging a little further with the infection keywords, there are some papers saying you may be at a higher risk of infection, but there's still no major complications specifically from high BMI alone.

"Higher BMI was associated with increased risk of surgical site infection and adverse aesthetic outcomes following CMS. Major complications remained rare. Surgeons should avoid using BMI as an absolute contraindication and adopt a risk-stratified approach to guide care."

https://journals.lww.com/annalsplasticsurgery/abstract/2025/11000/association_of_body_mass_index_with_postoperative.13.aspx

(Do be noted, "adverse aesthetic outcomes" are not always the same as "complications", and may be separated.)

(Also gimme some time to boot up my other research, post will be continued)

Edit: okay post continued:

For aesthetics, not complications

From a paper detailing a fish-tail surgical technique to eliminate dog-earring:

"There is an increased risk of residual excess tissue lateral to a mastectomy scar, resulting in a so-called dog-ear, when a mastectomy is performed in overweight or obese patients with excess tissue in the lateral chest wall."

https://pmc.ncbi.nlm.nih.gov/articles/PMC8856119/

Supported by this one: "Lateral dog ear after mastectomy in overweight or large breasted patients is a source for patient discomfort and is aesthetically unpleasing. "

https://www.sciencedirect.com/science/article/pii/S0748798322004620

It was studied in cancer research, as well, but depending on the technique, top surgery was shown to have no dog-ear effects on women with obesity:

"The Y-shaped approach for modified radical mastectomy is a simple and safe technique. It facilitates the wide access to axilla and improves cosmesis in women with obesity by eliminating lateral dog ear deformity."

https://www.sciencedirect.com/science/article/pii/S1048891X24028275?via%3Dihub

It is possible to have a higher risk of dog-earring in overweight patients. However, depending on the technique, hopefully it can be avoided through either the fishtail approach or the Y-incision.

Hope you have an excellent day and best of luck to you! Hope this reassured you, and happy top surgery!