The highlight feature of Google Photos was that it would let you upload unlimited photos and videos as long as they were compressed. This feature will no longer be available after June 2021, announced Google in a blog post today.
Following June 2021, Google Photos will apply the 15GB upload limit you get as a default on any Google account. Previously, this only applied to photos uploaded in full uncompressed quality, whereas there was no limit on uploading high quality compressed images. However, starting June next year, all photos and videos will count towards the 15GB limit.
Though keep in mind that this change will only apply to the data uploaded after June 2021 and anything added to Google Photos before that date will not be counted. After June 1, 2021, you will only be able to upload an additional 15GB, but after that, you will need to subscribe to Google One services to extend your privileges.
However, if you are inactive on Google Photos for more than 2 years, or have exceeded your upload limit for over 2 years, then Google may delete your content across multiple services.
If you happen to have a Pixel phone, you can continue to upload full quality images endlessly for years.