See backstory in bug #1932447 (Plasma is shipping a workaround, but I'd rather not have to do that long-term). Turns out systemd-managed user sessions currently ignore autostart/xdg-user-dirs.desktop due to https://github.com/systemd/systemd/issues/18791 One possible way forward is to swtich to a one-shot user systemd unit, like arch: https://github.com/archlinux/svntogit-packages/blob/packages/xdg-user-dirs/trunk/xdg-user-dirs-update.service
> One possible way forward is to swtich to a one-shot user systemd unit That would break things for everyone not using systemd user sessions, either by disabling it in their desktop's settings (e.g., startkderc for Plasma) or because their desktop environment does not support it to begin with. Unless both the autostart service and the systemd unit are shipped.