I now found and followed this:
https://blog.quindorian.org/2021/05/firmware-update-samsung-...
And it seems to have worked. After extracting this updater tool and running it, smartctl kept showing the old firmware version (3B2QGXA7), but after reboot it now shows the new version (5B2QGXA7).
I took the risk of running this while the OS (Archlinux) was running with the disk mounted (this is the OS install disk), and at first sight this didn't cause issues. But still do it at your own risk!!