It is no longer possible to upload photos to My Photo Stream at all. Apple has already disabled the upload of new photos - they are no longer uploaded to My Photo Stream at all. Just leave the photos im My Photo Stream, after you have saved them on your device. The remaining photos will vanish from My Photo Stream, when Photo Stream is shutting down on 26 July 2023. My Photo Stream does not count against your free cloud storage, it is a free service.
Once you have saved your photos, you could turn off My Photo Stream in th Settings, and not wait for Apple pulling the plug. Information about the My Photo Stream shutdown – Apple Support (UK)
"My Photo Stream is scheduled to be shut down on 26 July 2023.
As part of this transition, new photo uploads to My Photo Stream from your devices will stop one month before, on 26 June 2023. Any photos uploaded to the service before that date will remain in iCloud for 30 days from the date of upload and will be available to any of your devices where My Photo Stream is currently enabled. By 26 July 2023, there will be no photos remaining in My Photo Stream and the service will be shut down. "
My Photo Stream – Apple Support (UK)