File extension k9s seems not registered in android

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Expected behavior

If I select a k9s file on android, I want to open it with k9.

Actual behavior

I exported on the old android device the k9 settings to a cloud storage (nextcloud in my case)

Then I opened the file on the new android device.

Android gave me choice of some apps to open the file (with file extension k9s). But k9 was not in the list. That's very strange. I think it would be sensible if I can open a k9s file with k9 directly.

Environment

K-9 Mail version: latest from google play store