iCloud & iCloud Photos · Storage Studio and iCloud
Where can I see how much space Storage Studio freed from my cloud files?
Short answer: Run Tuhi's summary reports what its cloud step freed, and Background Activity (Job Insights) records how much was freed by keeping cloud files online-only, with when it last ran and any problems.
Right after Run Tuhi finishes, its summary includes what the cloud step did. Later, open Background Activity (Job Insights): the cloud job shows an entry saying how much it freed by keeping cloud files online-only, along with when it last ran and any problems.
The overall effect also shows in Storage Studio's free-space figures and in Storage Profile's Your storage over time chart.
If an entry says it couldn't finish making cloud files online-only, see what to do when cloud optimisation fails.