You can create a Boolean field compute that verify if a record was checked in your many2many. Then you make a condition based on your Boolean field for the visibility of myField.

Something like this:

is_visible = fields.Boolean(compute='_compute_visibility')

@api.depends('fieldm2m')
def _compute_visibility(self):
    for rec in self:
        rec.is_visible = bool(rec.fieldm2m)

In your xml:

<field name="is_visible" invisible="1"/>
<field name="myField" attrs="{'invisible': [('is_visible', '=', False)]}"/>