There's an ODK Collect v1.29 beta out now which no longer registers media with the Android Media Store. On some Android versions, file browser apps will still have access to the media files captured from Collect. However, those files should not be available when later browsing to select media from Collect. I think this is a really good change in line with other updates to how Collect data is stored so thanks for bringing this up, @Tino_Kreutzer.
If you think this behavior change could affect you, please try out the beta and give us feedback!