I have meta data to custom post "event", registered as non-single, i.e., there is an array od metadata "terms" (it is not WordPress term, I just call it term, it is a record containing start date of the event, end date of event and possibly start and end time of the event.

register_meta(
    \'post\',
    \'term_definition\',
    [
        \'object_subtype\' => \'event\',
        \'type\' => \'object\',
        \'description\' => \'object with time data of the event\',
        \'single\' => false,
        \'auth_callback\' => __NAMESPACE__ . \'\\authentication\',
        \'sanitize_callback\' => \'sanitization\',
        \'show_in_rest\' => [
            \'schema\' => [
                \'type\' => \'object\',
                \'properties\' => [
                    \'ID\' => [
                        \'type\' => \'integer\'
                    ],
                    \'startDate\' => [
                        \'type\' => \'string\'
                    ],
                    \'endDate\' => [
                        \'type\' => \'string\'
                    ],
                    \'startTime\' => [
                        \'type\' => \'string\'
                    ],
                    \'endTime\' => [
                        \'type\' => \'string\'
                    ],
                ]
            ]
        ]
    ]
)

I want to get all posts of my custom type event, where startDate in metadata is after current datetime (or before current datetime). From documentation, it seems this is only possible for single, simple metadata, as described in the handbook. As a sidenote, I noticed that metadata created in this way get serialized and stored in the database like so:

meta_key: \'term_definition\'
meta_value: a:3:{s:9:"startDate";s:19:"2021-12-09T16:36:00";s:2:"ID";i:0;s:7:"endDate";s:19:"2021-12-10T16:36:00";}