Both R-32 and R-454B have advantages/disadvantages over each other. R-32 is significantly cheaper than R-454B right now, because it's older, and the patents have expired, unlike R-454B which is newer and still patented. R-454B, however, has a significantly lower GWP, so it will be better poised to comply with regulatory requirements in the future, when the GWP limits ratchet down even more - which might make it cheaper in the long term, and prolong the time before manufacturers have to redesign their equipment again.
As said above, neither R-32 nor R-454B will be allowed for retrofit into R-410A units, because of the flammability.
Right now, there are no R-32 or R-454B central ducted systems available in the US. R-410A is still the only option. For mini splits, one R-32 unit is currently on the market. It's made by Daikin and it is available for sale in 4 states, which have updated their building codes to allow flammable refrigerants. The other 46 states still effectively ban flammable refrigerants outside of tiny applications like window units, mini fridges, etc.
EPA has not confirmed the final R-410A ban in new equipment yet, but when it does happen it is expected to be January 1 2025, which will line up with the bans in several states including California. R-410A equipment being banned in 2023 is outdated information and will not be happening. However, January 1 2023 will see the introduction of new efficiency standards for central AC, and the new SEER2 rating system, which is supposed to be more accurate at reflecting real life energy consumption in the field compared to the original SEER system. Northern climates will be effectively raised from 13 to 14 SEER (by today's ratings) with the rest of the country higher.
