Try using your numeric id (1958129) instead of your username (geralda). Seems to run pretty fast for me that way.
To find your own user number, go to your profile page, and it will be in the URL. Example: https://www.inaturalist.org/people/1958129
To find any other user’s number, go to their profile page, and hover over the Follow / Stop Following button at top. Their user number will be the “friend_id” in the URL. Example: https://www.inaturalist.org/users/1958129.json?friend_id=51061
FYI I commented in the feature request thread - this API parameter has never been implemented. There may be a little bit of the Mandela Effect going on here. A user made a comment on a post reference the parameter, but it did not exist at that time, nor any time previously or since. We’d consider adding it though.
Unfortunately the API isn’t terribly consistent with naming around implied logical parameters as this (the nots or withouts). This is something we’d hope to change if we released a new version of the API and allow negation of any parameter if possible, in a consistent way.