I have used OMV for years. Great system.
I remote in using zeroTier.
It’s installed on the OMV server, and I have it on all my devices.
That puts all my devices on a virtual “local network” so I can explore my shared folders, log into the OMV admin panel, etc, anywhere in the world.
Has been working beautifully for me, for years.
I hope that helps.
https://github.com/T8RIN/ImageResizer
Image toolbox on Android is phenomenal.
Does exactly what you needs, and a tonne more.