Where Is APT Finding That Old Proxy?
Deleting apt.conf does not remove every APT proxy setting. Inspect effective configuration, configuration fragments, and the command environment.
Start with the effective configuration and persistent declarations before removing another APT file:
apt-config dump
rg -n -i proxy /etc/apt/apt.conf /etc/apt/apt.conf.dapt-config dump shows APT's effective configuration; the search helps locate stored proxy declarations. A missing searched file is not itself an error to repair. Review output locally because values may contain credentials.
Deleting /etc/apt/apt.conf removes only one possible source. APT also reads fragments, accepts command-line overrides and supports proxy environment inputs. Check host-specific keys as well as the default using the configuration read rules.
If the old route remains unexplained, inspect the environment of the actual shell or automation launching APT. sudo can change that environment; the ordinary terminal's variables are not equivalent evidence.
For an intended direct comparison, use the documented DIRECT value for the relevant transport while accounting for more-specific host entries. An undocumented magic string called false in an old answer cannot establish the same policy.
Change the source owning the obsolete address. Keep unrelated files in apt.conf.d. If management software recreates the entry, correct its input so the proxy does not return at the next refresh. A desktop toggle cannot remove all these independent sources.