How can I have MBR and GPT separate dual boot drives?

My BIOS is currently set to Legacy. My ASUS laptop is from around 2014 running windows 8.1. I just bought a second SSD and want to install Linux. So I will have the option to dual boot into Windows or Linux as I choose.

I need to format the new SSD first, either as MBR or GPT. If I choose GPT it will not work in Legacy correct?

And if I change my BIOS mode from Legacy to UEFI will the windows SSD still work?

Also I cannot see any option to change from Legacy to UEFI in the boot menu.

Basically I would like to keep the windows drive as it is MBR and the new Linux drive as GPT and be able to boot either, is this possible?