There is many example in Odoo code, One of them in event email template:

t-set="date_begin" t-value="format_datetime(object.event_id.date_begin, tz='UTC', dt_format="yyyyMMdd'T'HHmmss'Z'")"/>

Another example in survey template:

type="text" class="form-control datetimepicker-input o_survey_question_datetime bg-transparent text-dark rounded-0 p-0"
       t-attf-data-target="#datetimepicker_#{question.id}" t-att-name="question.id"
       t-att-value="format_datetime(answer_lines[0].value_datetime) if answer_lines else None"
       t-att-data-question-type="question.question_type"/>