A group of Microsoft Products and technologies used for sharing and managing content, knowledge, and applications.
Dear Vanessa,
We understand that you want to share SharePoint site to external users who don’t have Microsoft account.
First, we would like to convey that we can share the site to external users. We need to add this user as Guest in Azure. Then we can add these external users as member so that they can upload files and collaborate with each other.
For your reference: Collaborate with guests in a site
You can refer to this article to know more information about it: External sharing overview
About the site storage limits, all the files store in the SharePoint Online will take the storage of this site no matter who upload to this site. The site owner and admin can go to SharePoint setting-> Storage Metrics.
Please contact us if you have any further question. Have a nice day! 😊
Best Regards,
Ivy