Most of the time, you can control where XDG puts its litter, cf. https://wiki.archlinux.org/title/XDG_user_directories

Just note that XDG_DESKTOP_DIR and XDG_DOWNLOAD_DIR can not point to the same directory or chromium will disregard your config.

P.S. Reader, if you can commit to chromium without much hassle, check this and fix: https://wiki.archlinux.org/title/Talk:XDG_user_directories

You (and other folks...) should probably click-through to the bugzilla links. Yes, normally. But, it looks like some legacy code path near the XDG stuff caused an accidental extra dir creation.

(I was rolling my eye wading in, thinking that Thunderbird was doing XDG and maybe some distro just wasn't setting XDG_CONFIG_HOME correctly, etc, but alas, no it's a TB bug)