What you describe is the stock Android recovery, not TWRP (see here for some TWRP screenshots).
You could try that again. Make sure after installing TWRP to directly boot into TWRP to let it make itself resident. If you boot Fairphone Open OS inbetween, it may replace the new TWRP with its own recovery again.
In Install LineageOS on FP2 | LineageOS Wiki this is point 6 in “Installing a custom recovery using fastboot”. Don’t miss it.