Without knowing your height, age, weight history, prior use of other GLP's etc etc it is a bit of a guess. Assuming you are of sort of tallish average male? height at 1.8m current BMI is still 39. You have lost 28 pounds or 13 kilos. This and the fairly short time frame should not be enough to cause drastic metabolic adaptation, so your daily calorie consumption will have dropped a bit from the weight loss but not enough on its own to stop it .
Usually at a BMI in that sort of range any reasonably low calorie intake of less than 2000kcal/day should cause some weight loss, even if you are fairly inactive.
I am also not sure how long your current weight has been static , if it is less than a month it could still be random fluid balance fluctuations rather than no further fat loss.
Also you are going to need to work out you calorie intake and output so you can understand what is going on. You really need to weigh every single thing you eat for a week or more to get an accurate picture , peoples' estimates are really inaccurate, and people often lie to themselves about how much they are eating, and then lie to themselves about lying to themselves.
Average weight loss from the most recent reta trial was about 29%, so you are not anywhere near that at around 9 to 10%, you could just be really unlucky , for every person who loses more weight than the average there has to be someone who loses less weight than average. The general lack of side effects does suggest you might have a lesser response than average.
Given you are using grey sourced peptides it is obviously possible you could be mis measuring your doses, so despite it sounding stupid I would strongly recommend double and triple checking your calculations and dilutions. Getting doses wrong is really common. It is also possible your reta is massively underdosed, so unless you know your batch has been tested it is likely worth getting another lot from a well known popular supplier, that ideally has a third party test already done on it , or even paying to get your batch or a new batch tested to be sure of what is going on with doses.
I would suggest going through all those considerations first before considering higher doses or combinations, it sounds like you are probably in the high risk weight range where higher doses or extra drugs are probably worth the risks, but without knowing sex, height, age and any other illnesses it is impossible to even start to consider it. There are no scientifically proven to be effective and safe treatments stronger than 12mg of reta, and even it is not officially approved yet. Getting some sort of medical checkup and bloods might be a good idea, in an ideal world you could get good medical advice first but that is not always possible.
After checking the other issues options would be a bit more reta, given you have few side effects this is not a bad idea. Or adding in low doses of cagrilintide and going up slowly in dose, starting at 0.25mg. or adding in low doses of semaglutide for extra GLP-1 agonism and extra appetite suppression.