SAT issued an official press release today (June 8th, 2022) which you can find here announcing an extension for the mandatory use of CFDI 4.0. The new date for it to officially displace version 3.3 is now January 1st, 2023.
SAT is also asking individuals and entities who already use CFDI 4.0 to continue using it and urging taxpayers who use version 3.3 to continue their transition process throughout the rest of the year.
They also explain that it is important for all taxpayers to know (and update if need be) the information on their Constancia de situación fiscal, as it includes identification, location, and fiscal obligations information such as:
Individual or legal name
Tax address zip code
Since this is precisely the information CFDI 4.0 automatically validates, they also remind taxpayers that if they know what it is for a fact, they can just give the information to their vendors or employers without having to turn in a Constancia de situación fiscal. Of course, the reason both vendors and employers have been asking to see the Constancia de situación fiscal is that that is the only way to be asbolutely sure the information is correct.
They also emphasize the fact that the obligation of issuing electronic pay slips is a separate obligation from that of paying employees' salaries and wages, so not turning this information in cannot be a reason to withhold payments or to fire an employee.
The press release also gives instructions for getting a Constancia de situación fiscal, point out that this is a free process and encourage people to report any acts of corruption if they are asked for money in exhange for a Constancia de situación fiscal or if they are witnesses to any kind of acts of corruption.
You can also find more information on what CFDI 4.0 is, among other things, here