One thing to be careful to avoid confusing is the difference between the actual text of the Missal of 1969 - the Ordinary Form or “Novus Ordo” that can be celebrated in English - and other changes in discipline or common practice that are not directly related to the Missal.
Example 1: Prayers at the Foot of the Altar and Last Gospel. These were actually removed from the Ordinary Form of the Mass and cannot be said as part of it. I don’t know why, but that’s the way it is.
Example 2: Kneeling at a communion rail to receive Holy Communion on the tongue from a priest. Kneeling to receive is relatively rare in celebrations of the Ordinary Form, and Extraordinary Ministers (lay people) and reception in the hand are permitted - but that’s not really a change to the Missal itself, but rather a change in practice. The Ordinary Form can be and sometimes is celebrated with the traditional ways of receiving Holy Communion. Same goes for Ad orientem for the Eucharistic Prayer/Canon.
Other things that are often absent from modern Churches or from celebrations of the Ordinary Form, but can still be used include: statues, High Altar, votive candles, Sanctus bells, Communion patens, burse, chalice veil, and pall and paten, Latin, and Gregorian chant. The Confiteor and Roman Canon are both optional and could be used all the time; the Sign of Peace is optional and could be omitted all the time. Incense also could be used any time.
I suggest you read the full text of the Order of Mass sometime. There’s not as much missing as you may think.