Order of operations for upgrade? Two internal drives, one running BigSur

Hello,

I have been running BigSur successfully for a long time, but I would like to attempt to update my OS to something newer.

I purchased an M.2 drive and have it installed. What I would like to do is once again attempt to upgrade using OpenCore.

My current OS is running (the install method that shall not be named) as it was the only way at the time I could get my OS up and running quickly after losing a week to failed OpenCore install.

However, I don't have time to dedicate days to this project alone, plus I have to keep my current OS running for work.

What would be the order of operations to allow me to work on upgrading when I have time, but avoid any downtime with my current OS, or risks of it not booting.

I also dual-boot to Windows.

Thank you!