Modernist do not accept the Traditional Latin Mass as a valid Mass because it is outdated in the modern world. Traditionalists, on the other hand, don’t accept the Novus Ordo Mass as a valid Mass, because during the reformation of the Holy Mass, under the leadership of Pope Paul VI during Vatican II, there were six Protestant Ministers who helped the reformation of the Holy Mass. That is why our mass today is similar to the protestants. Many people including bishops and priest doesn’t want this new form of the mass, that is why Traditional Priest formed a society that maintains the Traditional Way of the Catholic Church. In the previous centuries, the Holy Mass was prevented from any liturgical abuses, but the Novus Ordo Mass experienced some liturgical abuses like clown mass, liturgical dancing, clapping, laypeople giving Holy Communion and using rock instruments. But some Catholic priest maintains the Solemnity of the Holy Mass under its new form.
Now the current traditionalist tells others that the Novus Ordo Mass is invalid, and God is not present in the new mass. Is this true? Of course not! The Novus Ordo Mass is still valid and God is present during the Holy Mass including the Sacrament of the Holy Eucharist. May be some prayers and parts of the Holy Mass was changed but the Bread and Wine stills becomes the Body and Blood of Christ during the Consecration. But the grace that we receiving in the Novus Ordo Mass are less compared to the Traditional Latin Mass. Even the Society of Saint Pius X (SSPX) who are hated by the modernists agreed that the Real Presence of Christ in the Eucharist is in the Novus Ordo Mass according to their article about the New Eucharistic Miracle in Poland (https://sspx.org/en/news-events/news/new-eucharistic-miracle-poland).
If we are traditionalist who attend the Novus Ordo Mass or a modernist who attend the Traditional Latin Mass, we must give respect to the Holy Mass. Because the Holy Mass is where we give praise and adore God. If we have to kneel, we have to do it even if we are the only person to do it. If there are prayers that has an error, pray the correct one. If there are some liturgical abuses, pray what our Lord Jesus Christ said during His Crucifixion, “Father, forgive them, for they know not what they do.” Let’s not say that God is not present in the new mass, because that is not true. Even if there are errors in the Church today, God does not abandon His people. Poor Catholics who are very devoted but do not aware of these errors are still Catholics. God is good, he built the Catholic Church and forever remain His Church, that is why the Traditional Priestly Societies remain in the Catholic Church.