Open source theres
Pocket Paint in #fdroid, which lets you import and arrange, also draw, has layers, but no filters / effects on photos.
For filters & effects theres Litrato in the izzyondroid fdroid repo.
Finally, not open source, but Snapseed (which is now owned by Google) is real nice to use editing, filters etc. etc. But don't think you can bring together multiple photos/images
All of them have network which I don't need or want my image editing app to have— I block that nonsense
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