Cubase does not detect mics. It will allow you to load the input and output buses that were loaded by the driver for your audio interface (UR44). Your interface has enough inputs to allow for (3) mics. It would be your job to ensure your input and output buses are created in the audio connections menu and that these buses are assigned properly to your audio tracks.
I suppose it may be possible that the version of Cubase you have may only allow for a certain amount of simultaneous audio connections. So you should list what Cubase version you are using.
Getting the output of the (3) mics to Windows or OBS should be possible too. But, I’ll leave it to someone else who is more familiar with OBS to comment.