How to prevent duplicate data in a spreadsheet using a conditional formula

I want to restrict data that will be inserted into a spreadsheet, based on a field, with the condition that it not be entered more than once. This data will come from another spreadsheet that receives random data.
In the filter, which formula to use?

Hello there,

not sure if you can do it only with a filter.

Is the duplicate data randomly spread in the sheet or will it come in batches next to each other?

Simplest way is - before creating a new entry, search the sheet if it already exists and only create it if it doesn’t.