Use it as your “Straw Man” device. Put any app that you want on it (no SIM card) that you wouldn’t place on your Degoogled phone. Apps that you want access to, but don’t want to connect it to your phone number. I still wouldn’t put any Google Apps on it, but if you have a relative or friend with Instagram, I might install that one. Keep the audio/camera covered with tape, since Meta software evesdrops/peeps on you. Also remember to NOT allow any of these suspect apps access to your Contacts list, since they’ll farm info from your contacts.
Finally, you instead might want to keep it around to install some apps that aren’t installable on a Degoogled phone. Keep it around for the day Google Store slams its door.