If I never used My Photo Stream and took pictures which automatically went to iCloud, do I have to be concerned about My Photo Stream shutting down?

The photos saved in iCloud are safe , they will be not removed unless you delete them , if photo stream is shutting down you should not be concerned My Photo Stream - Apple Support

How My Photo Stream works with iCloud Photos

My Photo Stream uploads your most recent photos (except Live Photos) so that you can view and import them to another device, if you like. Photos are stored in My Photo Stream for 30 days and then are deleted from iCloud. To keep your photos stored in iCloud on an ongoing basis, set up and use iCloud Photos. iCloud Photos uploads all of your photos and videos to iCloud and keeps them up to date across your devices.

If you turn on both My Photo Stream and iCloud Photos on an iPhone, iPad, or iPod touch, photos that you take with that device upload to both iCloud Photos and My Photo Stream.

If you use another device with the same Apple ID that has only My Photo Stream turned on, photos that you take on that device upload only to My Photo Stream. They don't appear on any devices that have only iCloud Photos enabled.

Learn more about the differences between iCloud Photos and My Photo Stream.

Note : set up photo library Set up and use iCloud Photos - Apple Support