How to use Timeshift to backup EXT4 filesystem on a separate BTRFS partition?

I have seen several articles on similar topics, but none directly address my question/problem. First, I want to use Timeshift GUI rather than CLI. I have a single physical drive and want to install Linux Mint on an EXT4 partition and create a 20g BTRFS partition for backup images on the EXT4 system partition. Is it possible? Admittedly, I don't know much about any of this. But I do know I previously installed the OS on EXT4 and formatted a USB stick with BTRFS and there appeared to be no option to backup to that.