Shutdown of My Photo Stream means that the automatic photo syncing service from Apple is ending. For me, with over 13,000 photos stored on my computer and backed up to the cloud, it means I need to find another way to back up my photos. I might switch to iCloud Photos or explore other cloud storage options like Google Photos or Dropbox to keep my photos safe.
1. You can sync your pics/videos between your Mac and iCloud Photos (and to/from any iDevice as well); but you only get 5Gb free. Personal view coming: For the price of a "cheap" cup of coffee you can buy 200GB of storage for £2.99 (in USA $2.99) per month. NB the storage limit is for the total of all your data, not just photos.
2. The 13,000 pics/videos on your Mac can be protected by using Apple's own Time Machine. The only cost is the External Hard Drive (EHD). This backs up hourly, then weekly, then monthly etc.
In fact, Time Machine can be used with 2 EHDs if you are worried, as we all are, of a failure of that one EHD.
3. Dropbox costs you money given the size of your library and I believe Google is the same. Why spend money there when you can get 200GB of iCloud Storage and invest in one (preferably two) EHDs almost certainly for less. And they are all Apple-based!
When you sign up for iCloud, you automatically get 5GB of free storage. If you need more space in iCloud, you can upgrade to iCloud+.
support.apple.com
and
Automatically back up what's important: Photos, email, music, and more.
support.apple.com
Ian