Many Google apps have APIs that allow users to give third parties access to data and functionality. This is often used for logging in, but also for querying contacts, appointments in the calendar and many other options. However, there will soon be a major change that could exclude many applications. Apps classified as unsafe will no longer be supported from the end of May.
Presumably, many Google users use external services that have limited access to the Google account. If that’s the case, you should know about a change that has hardly been communicated so far and will take effect from May 30th: Access to the Google account will only be allowed for applications that support two-factor authentication. A login that only consists of the classic combination of user name and password is then no longer sufficient.
To better protect your account, starting May 30, 2022, Google will no longer support any third-party apps or devices that use your username and password to log into your Google Account. This deadline does not apply to Google Workspace or Google Cloud Identity customers. The effective date of this policy for these customers will be announced on the Workspace Blog at a later date.
It is difficult to say how many applications or users will be affected. Older applications, in particular, could be affected, which are reliably doing their job but are no longer being developed or where the developers “don’t feel like” implementing something like this. I think the screaming won’t be big until early June when some combinations of third-party apps and Google apps will stop working.