What images are you talking about? It's like you're showing us a picture of a dark room with the lights out. List the file names you have in bin/targets/. Usually there's an image you can easily dd onto your (removable) storage.
As per OpenWrt naming convention, images with 'sysupgrade' in the name can be flashed using the sysupgrade utility on OpenWrt. Those images you can use to upgrade an existing installation.
The factory images are meant for installations 'from scratch' - or from OEM firmware, when talking about networking hardware; yours is a SBC and those work differently.
unzip
openwrt-bcm27xx-bcm2711-rpi-4-ext4-factory.img.gz
and write
" openwrt-bcm27xx-bcm2711-rpi-4-ext4-factory.img "
to any sdcard with balenaEtcher(https://www.balena.io/etcher/)
you can reset to defaults with 'firstboot'
some minor gains with relation to disk usage
some additional backup and restore abilities ( files changed in /etc/ et.al. )
probably a little more 'path-well-tread' with relation to disk issues although with sdcards this point is largely mute (2c)...