Unable to install PopOS to flashdrive

[another4til7]

Distribution (run cat /etc/os-release):
Current

Related Application and/or Package Version (run apt policy $PACKAGE NAME):
Installer

Issue/Bug Description:
Attempt to install PopOS (burned to one thumbdrive) to a a second thumbdrive. Erase button never activates

Steps to reproduce (if you know):

1. boot off installer
2. insert target flash drive
3. select target flash drive and partition with a boot and root partition
4. select each partition and click "use partition"
5. button doesn't work

Expected behavior:
Button does work

Other Notes:
I need to test a fair number of packages and custom apps before installing on my live machine. And I need to make sure my trackball will actually be supported (works under Ubuntu 22.04 LTS... debian can't see it)