Buy it, put it in a garage, don't drive it, 50 years from now (Then, all vehicles available for sale will be autonomous electric, etc...) It will be worth a million dollars, regardless of model year. The Smithsonian will buy it for an exhibit titled "Ancient Modes of Transportation."
If you're one of those guys with more money than you know what to do with and you want to buy a new Bronco and ship it straight to storage as a "collectible," of course the 2021 is the one you want (and probably the First Edition at that).
For the rest of us mere mortals, it should make zero difference, aside from the 2022 finally offering some things the 2021 promised but couldn't deliver (as well as some inevitable bug fixes).
My take is this, the rarest production of the M21 year might be collectible or worth money, as long as it’s a manual. Manuals will be dead in the next 20-30 years. I’m saying if you’ve got a 2-door Badlands with a manual transmission and a cool color like Cyber Orange, you’ll have a vehicle worth some money in 20 years. I’m calling the color option and 2 door because in 20 years I think loud colors will be more rare and 2 door vehicles are already more scarce than 4 doors.
Buy what you like and are passionate about. Chances are someone else likes and is passionate about the same thing. If enough people like and are passionate about it then it will become collectable. Rarity helps, but there are alot of factors. Its almost impossible to look at a brand new high production vehicle and be able to tell its future value or collectability. If you are scared of diminishing the value of something that may or may not have any value in 20 yes, then you probably won't ever get to enjoy said vehicle.
Yes, the true collector's Bronco will be a 2021 First Edition in Lightning Blue with Black interior and black mod Hardtop. Mine is going straight into a climate controlled storage facility for the next 50 years. On second thought I think I'll use it as a daily driver ?.
Aside from really high end cars that you need to be on a list for because there are only a few made, most cars you would consider doing well as collector cars are just passing their original MSRP 20-30 years later in mint condition with very few miles. Add in inflation, upkeep, storage, and insurance and the owner lost a lot of money. This is not even considering the opportunity cost of not investing the money in other things such as an S&P index fund. So you basically won't make anything on either year. Since we know that they will be essentially the same, there won't be the one-year-only cool factor either, such as the '63 Corvette split window. I would say forget collectibility and drive what you like.