According to help menu:

-onion=ip:port
Use separate SOCKS5 proxy to reach peers via Tor hidden services, set
-noonion to disable (default: -proxy)

I would expect that if -proxy is set, but -onion is not, -proxy setting would be used for onion connections.

Instead, according to getnetworkinfo, the default Tor port (127.0.0.1:9050) is listed for onion, but ipv{4,6} both have the -proxy setting. I inspected the traffic and saw that indeed it is not honoring my -proxy setting.

Bitcoin Core Daemon version v0.17.0.1-9e87d82e7

OS: Qubes OS, Whonix 14 VM