I’m worried a doctor would say there's not enough fat under my chin/jaw for Kybella? (Photos)

It appears you have a small amount of submental fat under your chin that would respond well to either Kybella or other measures like CoolSculpt mini or even micro-liposuction. Kybella is an injectable treatment that uses deoxycholic acid to destroy the fat cells, creating a more defined jawline over time. Most patients require multiple treatment sessions, but I would need to evaluate you in person to create your personalized treatment plan.

Liposuction is a one-and-done procedure performed using local anesthetic. Micro-cannulas are very tiny and remove the fat from the area, leaving little or no scarring behind. Recovery typically takes a few days. Some may say it’s too early to treat the problem, but at this early stage you can treat it more easily before it gets worse… and it tends to do that over time. Instead, you can enjoy a lovely result now that will last for years. No matter which treatment you choose, make sure the doctor you work with is both board certified and highly experienced to ensure an optimal outcome.
 

Kybella does nothing for sagging and does very little for contouring of the neck and lower face.  my younger patients tend to use facetite, threads, and fillers to give them more contouring. and ongoing they do morpheus every 2-4 months, thermage and ultherapy twice yearly. (see link)
With significant neck sagging you would need a neck/face lift with muscle tightening (platysmaplasty). at the same time lasers (fraxel,  co2 or erbium( or microneedling RF (fractora, intensif) can be . performed to improve the crepe skin or wrinkles.  You need a formal consultation, as the neck can be treated with a combination approach:
1. micro needling and lasers for texture
2. botox, disport or xeomin to help platysmal bands
3. intensif or fractora RF microneedling for crepe skin and lifting
4. fillers like belotero, restylane silk, juvederm volbella to improve lines and folds
5. neck/face lifting if sagging is prominent or early starting +/- platysmaplasty (muscle tightening)
6. J plasma/Renuvion, thermiRF, inmode facetite for internal tightening
7. ultherapy and thermage for external tightening
8. regular Venus legacy, exilis ultra, or inmode forma treatments with facials to maintain tightness
9. PDO novathreads or silhouette instalift cone threads for lifting and long-term collagen production
see an expert for a full evaluation and treatment plan based on your individual situation and goals.
Best, Dr. Emer.

Most of the changes I see in your picture may berelated to the muscles when you flex your neck.Kybella won't change that. I suggest an in person consultation. You would like to avoid a situationwhere the area is overcorrected. Best wishes.