The short answer to your question is no.
There's a thread in the ideas forum about this issue. You can vote on this to try and improve the chances of Microsoft adding this feature in a future release.
In the meantime, a work around that some people use is to create O365 accounts, or a shared O365 account for those external customers that require access to your app.
Do you want to share an app with a user who is not existed within your Organization?
I agree with @timl's thought almost, if you want to share an app with a user who is not existed within your Organization, I afraid that there is no way to achieve your needs in PowerApps currently.
More details about sharing an app within PowerApps, please check the following article:
As an alternative solution, you could consider take a try to create a Guest account from your Organization for the external user, and then share the corresponding app through PowerApps to this Guest account within your Organization.
Please check and see if the following thread would help in your scenario:
More details about adding a Guest account foe a external user, please check the following article:
I want to share powerapp with user in organization that do not have office365/powerapp subscription. They were able to access the Survey created using Microsoft forms. They signed in using there credentials(orgnizations internal email service credential) to complete the survey.
What to do the same thing for PowerApp data entry form.
Microsoft Forms is the method I often employ to gather data from external users. However it is very basic compared with PowerApps.
As said above, there is no easy way to share a PowerApp with someone outside your organization. You might try this method, though its not easy nor fun for the user: