Magisk "not installed" after flashing it

I tried flashing Magisk to boot, recovery, and then both, but the Magisk app still claims “N/A”. This is an A/B type booter (Sony Xperia 1 V XQ-DQ54 pdx234), that’s why I flashed both boot and recovery.

Banking app complained about rooting and stopped working, so something changed. Then I tried flashing back the boot and recovery from the /e/ installation package, but the bank app stays broken even after un+reinstalling. I’ll be needing help for repair later.

When flashing boot, fastboot said "Writing ‘boot_b’ " - not sure if that’s relevant.
The model-specific /e/OS installation instruction has a section “Ensuring all firmware partitions are consistent” for “copying the contents of the active slot to the inactive slot” - maybe I need to do that again? Will it break anything I’ve got working?

Really I’m just trying to enable Camera2 API for GCam app. I wish there was a toggle switch for it in the settings.