Of course Modernism is a heresy condemned by the Church in the early 1900's. It has its roots in the late 1800's Protestantism in terms of new methods of interpreting the Scripture. This led to Protestants using what we now call the "historical critical method" to deconstruct the Scriptures to get back to the communities where the oral traditions associated with the written scriptures where placed into a written essay with a theology evolving from the community in which the oral proclamation originated.
This led Protestant Scripture scholars to apply this method to Jesus and to strip all theology and doctrine surrounding Him to get back to the actual historical Jesus without later theologizing that added layers of "myth" to Him and exalted Him when in fact He was just a bungler bouncing through Palestine and Israel and only gradually came to know for Himself if He was or wasn't God.
This liberal Protestant method stripped Jesus of His miracles and attributed them to natural or made up causes. It stripped Him of His virgin conception and miraculous birth. A hammer was taken to the Nativity. It stripped Him of divine knowledge and of being One with the Father. It stripped Him even of His resurrection (for if bones could be discovered, wouldn't Jesus still be Lord?) kind of nonsense was posited.Of course stripped of the resurrection, this stripped Jesus of the Ascension and Giving of the Holy Spirit. Then of course one could question the sacraments of the Church, the after life and ultimately become agnostic or atheists.
In reaction to this Protestant deconstruction of Jesus and the Bible, Protestants who had good sense reacted. But of course they have no Magisterium. So the Fundamentalist movement in Protestantism developed around the time of the 1920's.
Pope Pius X knowing what was going on in liberal Protestantism at the time and the influence this could have on Catholic academics sought to stop it in its tracks through papal authority.
I don't think this is the main problem for Catholic today, the heresy of modernism. And in fact the use of the term modernism is off-putting to us who are modern and we confuse what this means with our own understanding of how hip it is to be modern.
The biggest problem Catholics face today is Post-Christianity. Now don't panic when I use the Wikipedia resource to scissors and paste the following description for you:
Postchristianity is the belief that the loss of the Christian monopoly in political affairs, especially in the Global North where Christianity had previously flourished, will eventually lead its demise in favour of secular nationalism. It includes personal world views, ideologies, religious movements or societies that are no longer rooted in the language and assumptions of Christianity, at least explicitly, although they had previously been in an environment of ubiquitous Christianity, i.e. Christendom.
Other scholars have disputed the global decline of Christianity, and instead hypothesized of an evolution of Christianity which allows it to not only survive, but actively expand its influence in contemporary societies.
The decline of ChristianityUntil recently, the overwhelming majority of Christians have lived in White nations, allowing theorists to speak of an "European Christian" civilization; conversely, radical writers have seen Christianity as an ideological arm of Western imperialism. As a result, the loss of Christian influence in the West has led to beliefs of inevitable global decline of Christianity.
Thus defined, a post-Christian world is one in which Christianity is no longer the dominant civil religion, but that has gradually assumed values, culture, and worldviews that are not necessarily Christian (and further may not necessarily reflect any world religion's standpoint, or may represent a combination of either several religions or none). Generally, therefore, post-Christian tends to refer to the loss of Christianity's monopoly, if not its followers, in historically Christian societies. For instance, according to the 2005 Eurobarameter survey, the majority of Europeans (in general) hold some form of belief in a higher power, although relatively fewer point explicitly to the Christian God.
In his 1961 The Death of God, the French theologian Gabriel Vahanian argued that modern secular culture in most of Western Civilization had lost all sense of the sacred, lacked any sacramental meaning, and disdained any transcendental purpose or sense of providence, bringing him to the conclusion that for the modern mind, "God is dead".
Thomas J. J. Altizer and William Hamilton of Emory University, drew upon a variety of sources, including the aphorisms of Dietrich Bonhoeffer's Letters and Papers from Prison, and brought this line of thought to public attention in a short-lived intellectual movement of the mid-to-late-1960s among Protestant theologians and ministerial students. Conservative reaction on the right and social-advocacy efforts on the left blunted its impact, however, and it was quickly overlooked in favor of more ethically-oriented movements such as the Social Gospel and feminist theologies, within mainline Protestantism.
My final comments: Our problem today is post-Christianity not modernism, post-Christianity may well flow form the modernist mentality.