2 years ago in a fit of cloud Panglossianism, I bought a 128GB Macbook Air.
After using every optimisation trick, uninstalling a bunch of bloated Adobe apps, and empyting 2GB of browser cache, I might just have enough space to upgrade to Big Sur
Thanks for all the tips. I tracked down another 5 GB thanks to Ross's suggestion of Disk Inventory X. Clearly Dr Pangloss never had to tangle with Excel logging bugs https://answers.microsoft.com/en-us/msoffice/forum/all/huge-excel-log-file-on-mac/5fdea038-a4b3-401b-a509-e72f75d60275