marcobio2 wrote: … I have downloaded my pics from the Photos Library on an external drive to decrease my iCloud storage.
That could mean several things-- how did you do this? Did you download from iCloud Photos? Did you export pictures from your Mac? Did you make a copy of your Photos Library?
You may want to think about how you backed up your pictures. If you have cropped, commented, or edited pictures, then there are really two versions of each picture-- the original unmodified file, and the edited picture. As long as an edited picture is in Photos, it can always be reverted to the original for different editing. If you've only backed up the edited version, then the edits are stuck forever. You may want to save both versions before deleting anything.
Do you use "Optimize Photos Storage" on your Mac? If you do, then you can't back up from the Mac, since it won't be keeping the full originals. If you have "Download Originals" chosen in Photos' Settings>iCloud, then you can make a copy of the Photos Library (likely in your Pictures folder) to get the complete backup.
For me, I never use "Optimize" on my Mac, because I want to be able to do a full backup of the Library. But I have the space for that luxury.
Can I now safely delete all pics from iCloud and then safely view them on my external device afterwards?
That might depend on how you backed up your pictures. If it were me, then I'd keep a copy of the originals pictures, and I'd keep a copy of the Library. And I'd keep copies of these on two different drives, because I fear hard drive failure, even though that is quite rare. You should read this, especially about formatting!
Move your Photos library to save space on your Mac - Apple Support
What should I be careful about before deleting the pics on iCloud?
First, you should be sure you have two copies of your Photos Library off your Mac.
If your Mac is connected to iCloud, then iCloud Photos is a complete copy of the Photos Library on your Mac, and they're kept exactly the same. So you should delete the pictures on the Mac-- that will delete them at iCloud and on your iPhone.
You've copied that Library to two places, by now-- right? And since you've deleted all the pictures on your Mac, it's empty and ready to accept more as you take pictures on your phone.
I also created a new Photos Library to upload new pics on the Cloud. How to make this one visible on my iPhone?
If iCloud Photos is empty, then your original Library is empty-- there's no need for this new one.
In any case, to be connected to iCloud, a Library must be designated the System Library in Photos' Settings>General, and iCloud should be turned on in Photos' Settings>iCloud.
We're here, if you have questions…
