If you get a message like this:
Or a complaint about MacOS running out of space AND you run OneDrive you need to switch on File On_Demand - got to OneDrive preferences and switch it on:
Another way to reduce space usage on a Mac is to not use the Outlook program; it is notorious for consuming disk space and a 120Gb SSD drive will be filled up very quickly. You can use the online version of Outlook here: https://outlook.office365.com