Transferring Data From Old Switch To New

Hi, I recently bought a new Switch and am waiting for my MicroSD card to come in the mail. I started a new game on Animal Crossing on the new Switch since I plan to delete my old game and was wondering, will the transfer of my games and save filed kill my new game on the new Switch? I'm going to delete my old Animal Crossing data before the transfer but, I was wondering what would happen. Has anyone done this before?

@meganorm64: it will delete the new data unless you back it up with Nintendo Switch Online because it will delete everything on the new switch. Sorry to hear about your island...

Yes there is a backup feature. When booting into the game, spam - (Requires online and most recent version of ACNH)