This warning, for a LUKS-encrypted system as configured by the Debian installer, is spurious. The initrd assumes it should be looking for lvmetad—it shouldn't be, but it doesn't realize that. The correct thing to do here is not to remove the warning as Teemu Likonen suggested—if your configuration requires lvmetad to be running and it isn't, you don't want the initscripts to fail to inform you of the simple and obvious reason it's not working. The Debian Way would be (and is—note Teemu's suggestion dates to 2016 and the warning remains, as does this open bug report) to leave the harmless warning alone since under a more complex LVM setup, it wouldn't be harmless.
If you know you don't need lvmetad for your lvm setup (and for just basic LUKS you don't), you teh internets say you can edit /etc/lvm/lvm.conf and "use_lvmetad = 0", then rebuild your boot config (update-grub or whatever) to disable trying to find it. In buster/sid, that's now already set and there's a comment that the setting is now unused because lvmetad itself is no longer used/provided in the Changelog. As for cryptsetup not working from the installer, that's because cryptsetup isn't installed in the installer environment. It's available as an "extra module", a udeb package, installable from the main installer menu. Unless you're using the advanced installer, you won't normally see that unless you interrupt the "guided" process and go back. It can also be done by hand, but that's honestly not well-documented and I don't recommend it to people who post hate-filled screeds about how garbage something is because they didn't bother to learn how it works first. Assuming you didn't just decide that arch or something makes you more l33t anyway, I'd recommend either using the live installer which provides a proper userland rather than an ultra-limited barebones repair console, or using the installer's menu system. Joseph Just a user who doesn't speak for Debian
