only way i have ever gotten pinball FX from epic to work with epic services activated (so you are online and can submit scores to leaderboards) and do table launch is by using legendary but if your cabinet is always offline just link to epic's version exe directly as thats much easier but if you want to be online and have online score submission try this :
Basically you can use legendary https://github.com/derrod/legendary to do this.
First you download legendary.exe from release somewhere and run a cmd prompt.
Then you normally do legendary auth to authorize yourself with epic games,
once authorized you normally do legenday list to find the pinball FX game's appname but i know it's 56a31432931740cdb0112d237d7d65aa
so what i did then is import my current Epic's pinball FX install location ("i:\Games\Epic Games\PinballFX") using
legendary import 56a31432931740cdb0112d237d7d65aa "i:\Games\Epic Games\PinballFX"
it should say it imported the game fine
Once that is done you can launch the epic version using legendary using following command to launch wild west rampage table in classic mode
legendary launch 56a31432931740cdb0112d237d7d65aa -Table 75 -GameMode Classic
and basically thats the command you use in your frontend as well.
Or you could also check which command legendary uses to make this work by running
legendary launch 56a31432931740cdb0112d237d7d65aa --dry-run -Table 75 -GameMode Classic
and it will show you the parameters it passes to pinballfx.exe intermediatary launcher (for unreal engine games), suffice to say never share that commandline with anyone as it will contain login credentials
you only need to do the import and auth once (unless you get logged out or so) and then you can always do the 3rd launch command and use that in your frontends
in theory once you did the authorization and import of the game you can then use always the last command to make it work from within pinballx but i never bothered with that. Steam version is way easier to use and i switched from epic to steam at the time early access ended