SharePoint lists allow items to have attachments, but there are limitations to consider (i.e. can't apply document management, versioning, or metadata on attachments). See Why you should never attach documents in a SharePoint list for more details, how to manage your list settings, and alternatives.

To disable the ability to add attachments to a list entry, site owners can:

1. Go to the site and click into the desired list.
2. Select the gear icon (top right) > List settings.
3. Select Advanced settings.
4. Under Attachments, select Disabled. 
   • To undo this action, select Enabled.
5. Scroll down and select OK. If prompted, select OK.