Novak Djokovic missed all events in the US last year as he could not enter the country legally due to his unvaccinated status and there is a chance it happens again.
Djokovic really hoped to leave behind COVID-19 restrictions in 2022 but some of them might follow him into next year as well. There is a chance Djokovic won't be able to play in Indian Wells and Miami like last year as the US seems likely to impose restrictions due to the spike in cases experienced in China.
They could join countries like South Korea, Malaysia, India and others that have already imposed new regulations about who can and can't enter their countries. The US seems likely to follow suit but it's not an official decision yet.