Freedom UI Detail List inline adding record - set Lookup column default value

Here is a code sample on how I solved it, maybe it helps somebody:

handlers: /**SCHEMA_HANDLERS*/[
    {
        request: "crt.HandleViewModelAttributeChangeRequest",
        /* The custom implementation of the system request handler. */
        handler: async (request, next) => {
            if (request.attributeName === 'GridDetail_u6gv7vy_ActiveRow') {
                const activeRowId = await request.$context.GridDetail_u6gv7vy_ActiveRow;
                const gridDetail = await request.$context.GridDetail_u6gv7vy;
                const defaultType = await request.$context.SWGLookupFileType;
                gridDetail.forEach((item) => {
                    if (item.attributes.GridDetail_u6gv7vyDS_Id == activeRowId
                       && !item.attributes.GridDetail_u6gv7vyDS_Type
                       ) 
                    {
                        item.attributes.GridDetail_u6gv7vyDS_Type = defaultType;
                    }
                });
            }
            
            return next?.handle(request);
        }
    }
]/**SCHEMA_HANDLERS*/

Please change "GridDetail_u6gv7vy" name to your list name and also attribute names ("item.attributes.GridDetail_u6gv7vyDS_Id" or "GridDetail_u6gv7vyDS_Type").