Pass --disable-privsep to configure script to eliminate dhcpcd start warning message: no such user dhcpcd. Or create dhcpcd user automatically.
Thanks for your bug report. I sent a patch to create dhcpcd user: https://patchwork.ozlabs.org/project/buildroot/patch/20201226171745.2414764-2-fontaine.fabrice@gmail.com/
Fixed in git: https://git.buildroot.org/buildroot/commit/?id=9e20f0910902d3f2af2c8fd0b44110d088ebc1e1 And the fix will be included in the upcoming 2020.11.1 release as well, thanks.