Fortnite app constantly crashes

that is the nature of beta stoftware you are helping apple test an unfinished product

report the issue to the beta program bug reporting channel and they can resolve it if its not something

which needs to be resolved in the next update for the fortnite app which will likely be released when ios13 become released

https://developer.apple.com/bug-reporting/

If Fortnite doesn't support beta it wouldn't matter if you had a developer beta or public beta.

Hopefully you made a iTunes backup to return to IOS 12.3.1.

No one here can help with any public beta software.

It is against the NDA you agreed to when you signed up to use the iOS 13/IiPadOS beta software.

If you need help, use the iOS developer forums and for Fortnite, contact the developers.

No one in these communities will never be able to help you with this here.

Sorry & Best of Luck to You!

There's nothing anyone here can do to help you. YOU chose to download beta software and that's the nature of the beast. You are testing it and you have a report a bug link you received when you signed up.

This is why I NEVER beta test. I don't want anything to not work and I'm perfectly capable of waiting till the bugs are out and the official release happens.

Be sure to contact Fortnite for a fix.

The same thing is happening to me. On iOS 13 beta 2. Any public match I get into it crashes

See my above post reply.

But will I be able to switch from dev beta to the next public beta

This isn't the place to be asking anything about beta software. I'm sure when you signed up to be a tester, they must have provided somewhere you should go, but this isn't the place.