Can masked text be recovered?

No. Masking is one-way. Keep the original file elsewhere.

No: a name has no shape to find. A column headed like a name (Name, Full name) is hidden whole from the start, and one click shows it again; any other column can be hidden whole too.

Can one finding stay as it is?

Yes. Open the list of what was found and untick it.

Mask a customer list before handing it over

Before an outside analyst or another department gets the file, hide the columns that identify people.

Open “Mask personal data”

Steps

Drop the CSV on "Mask personal data".
Press "Hide all personal data" or "Contacts only (email, phone)"; whole columns can be hidden too.
Check the preview table and save. The original stays as it is.
Save the processing report for a record of what was masked: kinds, counts, whole columns and the style (never the values).

Questions

Can masked text be recovered?: No. Masking is one-way. Keep the original file elsewhere.
Can names be found?: No: a name has no shape to find. A column headed like a name (Name, Full name) is hidden whole from the start, and one click shows it again; any other column can be hidden whole too.
Can one finding stay as it is?: Yes. Open the list of what was found and untick it.

The CSV is never uploaded; everything runs in this browser.