El Salvador making bitcoin legal tender, and the Strike / Bitcoin Beach / LN-enabled Chivo wallet was the largest bitcoin development in 2021, in my opinion.

I think Cash App adding Lightning support is shaping up to be the largest bitcoin development in 2022.

Not just because this instantly enabled 70 million prospective users for each and every Lightning network wallet and service, but because now all the other exchanges that have been resisting Lightning with their collective might are going to have to add LN or lose marketshare to Cash App and Strike.

The list of Exchanges with support for Lightning Network, while expanding, is still just a fraction of all the exchanges out there.

Exchanges with support for Lightning Network https://github.com/cointastical/Exchanges-With-LN