Hi,

In Odoo 19, the datepicker defaults to MMM d (e.g., Sep 18) because it uses the Luxon library with localized formats, which can be confusing compared to the old MM/dd/yyyy. You can change this by editing the Language → Date Format in settings, but the picker may still show abbreviated months. The most reliable fix is a small JavaScript override in a custom module to force MM/dd/yyyy it everywhere.

Hope it helps

we have develop app which force odoo to convert all month in number instead of month name.

https://apps.odoo.com/apps/modules/19.0/yt_numaric_date

Hello

I will give you a "Quick and Dirty" fix, based on the fact that this UX/UI change is a major drawback and that everyone should be free to choose whatever date format he/she prefer instead of being forced to use this "mmm dd" format

Also Odoo is open source so solutions to major and broad problems should be freely shared instead of being gatekeeped behind paid services or paid apps on Store

Please note that this fix is rather experimental but works even in SaaS version (does not require on-premise or Odoo.sh)
Also it should be quite safe to put in place as it uses a Try/Catch mechanism, ensuring it cannot break your Odoo instance even if the script fails

• Enable Dev mode
• Navigate to Views
• Search "Web layout" view
• In the "Inherited views" tab, create a new view with this code inside : 

<xpath expr="//head" position="inside">
    <script>
        try {
            (function() {
                owl.whenReady(function() {
                    try {
                        // Patch vue form - getFormattedValue
                        // Odoo v19 : Luxon écrase le format de date défini dans les settings de langue
                        // dateField.getFormattedValue utilise un binding statique, patch via prototype
                        var m1 = odoo.loader.modules.get('@web/views/fields/datetime/datetime_field');
                        if (m1 &amp;&amp; m1.dateField &amp;&amp; m1.dateField.component) {
                            var proto1 = m1.dateField.component.prototype;
                            proto1.getFormattedValue = function(valueIndex, numeric) {
                                if (numeric === undefined) numeric = this.props.numeric;
                                var values = this.values;
                                var value = values[valueIndex];
                                if (!value) return '';
                                if (this.field.type === 'date') {
                                    return value.toFormat('dd/MM/yyyy');
                                }
                                return value.toFormat('dd/MM/yyyy, HH:mm');
                            };
                        }

                        // Patch vue liste - registre formatters
                        // Le rendu readonly en liste passe par le registre Owl formatters, pas getFormattedValue
                        var reg = odoo.loader.modules.get('@web/core/registry');
                        if (reg &amp;&amp; reg.registry) {
                            var formatters = reg.registry.category('formatters');

                            var origDate = formatters.get('date');
                            if (origDate) {
                                var patchedDate = function(value, options) {
                                    if (!options) options = {};
                                    if (!value) return '';
                                    if (options.numeric) return origDate(value, options);
                                    return value.toFormat('dd/MM/yyyy');
                                };
                                patchedDate.extractOptions = origDate.extractOptions;
                                formatters.add('date', patchedDate, { force: true });
                            }

                            var origDatetime = formatters.get('datetime');
                            if (origDatetime) {
                                var patchedDatetime = function(value, options) {
                                    if (!options) options = {};
                                    if (!value) return '';
                                    if (options.numeric) return origDatetime(value, options);
                                    return value.toFormat('dd/MM/yyyy, HH:mm');
                                };
                                patchedDatetime.extractOptions = origDatetime.extractOptions;
                                formatters.add('datetime', patchedDatetime, { force: true });
                            }
                        }
                    } catch(e) { console.error('Erreur date patch:', e); }
                });
            })();
        } catch (error) {
            console.error('Erreur date patch outer:', error);
        }
    </script>
</xpath>

Should do the trick. Please note the code is set up for a dd/mm/yyyy (so European) date format. Changing to mm/dd/yyyy shouldn't be too complicated

Eliott