As the web-editor generates a 'static' html snippet stored in the database, it is not evaluated when loaded. So this 'quick trick' uses client javascript.

Made the country name available : (whichi is used as the option.text() )

class Http(models.AbstractModel):
_inherit = 'ir.http'


@api.model
def get_frontend_session_info(self):
session_info = super(Http, self).get_frontend_session_info()
session_info.update({
'geoip_country_name': request.session.get('geoip', {}).get('country_name'),
})
return session_info 

And using that i set the country in the form to the country found by geoip:

/** @odoo-module */

import { session } from '@web/session';

$(document ).ready(function() {
const slct = $('select[name=country_id].s_website_form_input');
if(slct.length){
if (session.geoip_country_name){
$('select[name=country_id].s_website_form_input option').filter(function(){
return $(this).text() == session.geoip_country_name;
}).prop('selected',true);
}
}
});

Enhancements: pass on the country database id for the country record, as those numeric values are used as the option.val()

Anyway, perhaps it is helpfull for someone else.