[Solved] In Rekordbox 4.2.1, why would Grid button be greyed out?

Have you linked the players with ProDJ Link to rekordbox? If yes - Grid doesn't work when the players linked but you should get a message about it.

This is when the Players are linked:

Second possibility is that your file is protected in rekordbox to prevent changes by mistake. In that case you need to unprotect it first.

In that case you need to unprotect the file.

The problem was player was linked to rekordbox. All is good now. Frank, thank you for your help.