Hi @NigelP ,
Do you want multiple users to be able to edit same PowerApps app?
Do you want multiple users to be able to edit same PowerApps app at same time?
If you just want multiple users to be able to edit same PowerApps app, I think the "Share" functionality within PowerApps could achieve your needs.
On your side, you could consider share your app with other end users with Co-Owner permission, then other end users could also edit your app.
More details about sharing an app within PowerApps, please check the following article:
https://docs.microsoft.com/en-us/powerapps/maker/canvas-apps/share-app
If you want multiple end users could edit same canvas app at the same time, I afraid that there is no way to achieve your needs.
Currently, within PowerApps, it only allows single one person to edit same app once time. If the multiple users edit same app at the same time, the rest of users would face Conflict error.
Best regards,