What surgical procedure would be recommended for my sagging neck (Age: 30)? (photos)

Based on your age and phots submitted, as well as you prior history of neck/chin lipo, I would recommend a more invasive central necklift procedure where a platysmaplasty and direct fat removal and contouring is done. This will nicely sharpen your neck and jawline contour. This is a short outpatient procedure done through a center incision under your chin without any need for an incision behind you ear.

Thank you for your question and sharing your photograph.
The photograph suggests that there is no laxity but rather volume deep to the platysma muscles which has not been addressed by liposuction because liposuction works on the fatty tissue situated under the skin and on top of the platysma muscles.
The anterior neck lift also referred to as short scar neck lift can address the deeper seated fatty tissue under the chin in combination with reduction of the digastric muscles and lower part of the submandibular glands which together contribute to the volume that concerns you.

Thank you for your question and photo. You may benefit RF microneedling treatments to tighten and contour sagging skin while improving its elasticity. This non-surgical option uses radiofrequency energy to encourage your body’s elastin and collagen production, resulting in a tighter and firmer appearance. Horizontal banding on the neck can also be addressed with Botox injections that target the large muscle in the neck known as the platysma muscle.
If submental fat is a concern, you could also consider Kybella injections. This treatment uses deoxycholic acid to dissolve fat cells under the chin to create a more contoured jawline. I recommend scheduling an in-person consultation with an experienced, board-certified facial plastic surgeon or injector. They will be able to discuss your concerns with you and determine the best course of action.