How can I add space to my Mac?

if you have an intel mac, you may be able to find a professional that can swap in a larger capacity drive. and that likely won't be cheap. if it's an M1 mac, the internal drive CANNOT be upgraded.

the best way to increase storage is by buying external HDDs or SSDs.

The Internal Drive has a Defined Capacity and adding space to the Drive can not be done.

need more storage space for my I cloud email