As Oliver mentioned, you can setup so that anonymous users are able to create records. With the new licensing of PowerApps Portals, you prepay for a set number of authenticated logins or anonymous page views.
Note that having anonymous creation allows for abuse - you may want to consider utilizing CAPTCHAs (can be setup for only anonymous users - see documentation here), if anonymous access is absolutely necessary.
Note that it's a lot easier to setup local (or, more preferably, Azure B2C) users so that you have some semblance of control on who creates records.