Best way to capture 4K while sending to ATEM?

I'm very new to this system and bought an ATEM Mini Pro ISO this week. My setup is three cameras, the main one is Olympus E-M10 iii which is set to record 4K@24. I'd like to use it as an 1080p for live streaming, but use the 4K footage for later edits. My question is what is the best way to do that? will it work if I connect it to a 4K external recorder like the Atomos Ninja and then send the hdmi output from the recorder to the ATEM? is there an alternative solution?

I think you should be able to record 4K internally on the camera and set the camera's HDMI output option to 1080p in order for it to send an HD signal compatible with the ATEM Mini.

And that might be your only option actually as the manual for that camera seems to suggest that it is only capable of 4K output over HDMI in playback mode, but is limited to 1080p output in record mode.

With a camera that is capable of 4K live output over HDMI, you could send it through a Ninja V (if you wanted to record in ProRes), as the Ninja has an option to downscale the HDMI output to 1080p.

Thank you very much, Dave!
It looks like the only solution. Now the problem is that my camera is limited to internally record 30 minutes at a time. All signs lead to getting the gh5 or gh6...

That's exactly what I do with my new Canon XA50's - record in camera at 4K & output to HDMI at 1080p & it works a treat.
My older retired 4K panasonics couldn't do that so i was limited to recording in 1080 when live streaming, hence replacing them.
Cheers. Paul