Updating a large sheet - Mass Move or Delete

Hi all,

New to SS so please excuse if this is a very basic question.

We have a lookup sheet that contains around 20,000 rows of data and has Match functions that point to it from other sheets, due to this I do not want to just delete the sheet and create a new sheet each time, then have to go back a recreate the MATCH functions. The lookup sheet needs to be updated once a month with new data.

There seems to no way, auto or manual to delete this many rows. If I select all the rows manually, SS tries, then after a min or so, errors, asking me to not save and refresh. Is there anyway to merge or mass delete in SS? I have even tried to use automation whereas I would I would create a form with a check box, then trigger when the checkbox was checked AND another cell had data to use the move automation, however it seems I need to select a unique value.

This seems the most basic function so where am I going wrong??