I’m just going to cut and paste the text of the email here. TLDR version is all your existing high quality photos are free and will remain free, any new ones going forward count against your storage limit.
Email and pic of it down below
We launched Google Photos more than five years ago and since then, it’s become more than just an app to manage your photos. It’s become a place you go when you feel nostalgic and want to reminisce. Today, Google Photos is the home for more than 4 trillion photos and videos, including yours, and a remarkable 28 billion new photos and videos are uploaded every week. In order to welcome even more of your memories and build Google Photos for the future, we are announcing a change to our storage policy.
Starting June 1, 2021, all new photos and videos backed up in High quality will count toward the free 15 GB of storage that comes with your Google Account or any additional storage you may have purchased, the same way other Google services like Google Drive and Gmail already do.
All photos and videos you back up in High quality before June 1, 2021 are exempt from this change and will not count toward your Google Account storage. This includes all of your existing content uploaded in High quality.
We don’t take this decision lightly and we acknowledge that this is a big shift, so wanted to let you know well in advance and give you resources to help you navigate this change.
Do I need to do anything right away?
No, you can continue to use Google Photos to back up your photos and videos. After June 1, 2021 we will reach out and send you reminders when you are nearing your storage limit. Most users will have years before they need to take action.
When will I reach my free 15 GB of storage?
We created a personalized estimate that shows how much time you have until you reach your quota. This estimate takes into account how frequently you back up photos, videos and other content to your Google Account.
What can I do to manage my storage?
On June 1, 2021, we will be launching a new storage management tool which will help you easily find and delete dark, blurry, and otherwise unwanted content. You can also purchase more storage with Google One where available.
We are grateful that you choose Google Photos to safely store your memories. This change enables us to keep up with the growing demand for photo storage and remain focused on building Google Photos for the future. To learn more about this change, check out our Help Center article or Blog Post.
Your Google Photos Team