Exactly ZERO countries have even recommended a 4th dose for the general population (although some of allowed 4th doses for immune compromised individuals).
The claim most likely originates from the fact that some countries permit the 3rd dose to be administered as early as 3 months after the second dose.
It is widely accepted that following a second dose, neutralizing antibodies drop off significantly over the next 6 months or so, while cellular immunity (primarily responsible for protection against severe disease) remains strong with very little decline of effectiveness.
Many countries are in the midst of a campaign to deliver "boosters" or "3rd doses". These terms are often used interchangeably, but over time, we will learn which is the more appropriate term. There is good reason to believe that the immunity afforded by a third dose will be stronger and more durable than the second, suggesting that the vaccine should be a 3-dose series rather than a 2-dose series.
It is very much unclear whether and how often we will need boosters in the long term to maintain sufficient immunity.