Mirrored Data got removed together when Data in Source Board got deleted

Seeking any advice, appreciated. I mirrored a column from Board A to Board B (connected the 2 boards, one way). However when I remove the data from Board A, the mirrored data in Board B also got removed. Try restricting edit for the column in Board B, but issue persist. I need the mirrored data as a reference for Last Used Date, hence need the date to stay in there. Any option using Monday.com’s automation. Many thanks!