There will be so many events you can put it off for Christmas, easter, birthdays, party, hen do, holidays, work dos, weddings where you want to "enjoy yourself".
You need to work out if your priority is to treat your obesity and improve your health, while enjoying yourself but in a different way to before, or to continue to eat excessively and continue to gain weight.
You don't know how you will respond to Mounjaro. It might not impact your appetite at all until you are a few months in and on higher doses, you might be a fast responder on the lowest dose, you might have no side effects, or you might have unpleasant ones..............or anywhere in-between.
You won't know until you try, but if you go in with the mindset you need to eat and or drink excessively to enjoy yourself perhaps you need to reflect on that more before starting/investing in yourself. Would you put off a medical treatment for any other condition if you couldn't drink because of it?
Christmas last year for me (6 months into MJ) was - enjoyed the occasional chocolate, but didn't miss not having the whole tin, for Christmas dinner had a light prawn starter, a protein focused main (lots of lean meat and veg, but less pigs in blankets, roast potatoes, sausage meat etc), and a tasty but small dessert. I had one glass of wine, didn't fancy more. It was a lovely meal and I really enjoyed it, I didn't feel like I had missed out when everyone else was gorging and groaning. I did find the snacking habit was starting to creep back in over Christmas and had to bring that back under control in January.
You could start now and depending on how you feel, stay on the lower doses over Christmas, potentially skip a week.