It's pretty easy to apply seccomp to a process using systemd by adding SystemCallFilter= in its unit file. There's a reasonable set of permitted syscalls for general system processes, aptly called `@system-service`, but you can tweak that to suit your needs [1]. I generally use this, among other settings, to further lock down system services [2].
[1] https://www.freedesktop.org/software/systemd/man/latest/syst...