Heresy is simply the rejection of specific doctrines while still claiming to be faithful to the Church.
So any Catholic that "denies the sin of homosexuality" is obviously a heretic.
There are, therefore, two ways of deviating from Christianity: the one by refusing to believe in Christ Himself, which is the way of infidelity, common to Pagans and Jews; the other by restricting belief to certain points of Christ's doctrine selected and fashioned at pleasure, which is the way of heretics.
— CATHOLIC ENCYCLOPEDIA: Heresy
According to Catholic teaching, what is the status of a priest who does not agree with the Church's stated teachings on homosexuality and gender?
The short answer is that such a priest would be heretic and a dissenter at the same time.
The Catholic Church makes a distinction between 'material' and 'formal' heresy. Material heresy means in effect "holding erroneous doctrines through no fault of one's own" due to inculpable ignorance and "is neither a crime nor a sin" since the individual has made the error in good faith. Formal heresy is "the wilful and persistent adherence to an error in matters of faith" on the part of a baptised person. As such it is a grave sin and involves ipso facto excommunication; a Catholic that embraces a formal heresy is considered to have automatically separated his or her soul from the Catholic Church. Here "matters of faith" means dogmas which have been proposed by the infallible magisterium of the Church and, in addition to this intellectual error, "pertinacity in the will" in maintaining it in opposition to the teaching of the Church must be present. - List of heresies in the Catholic Church
Dissenter is a modern term used by heretics to make heresy sound more acceptable to modern like minded individuals.
The Code of Canon Law defines heresy as “the obstinate denial or doubt, after baptism, of a truth which must be believed by divine and catholic faith” (canon 751). The Catechism of the Catholic Church identifies heresy as a sin against faith and thus against the First Commandment (CCC 2089)
Over the past few decades heresy has become institutionalized in many Catholic institutions, from colleges and universities to hospitals, from magazines and periodicals to chancery offices. Many use the broader term dissent to express an attitude of opposition to official Church teaching on a spectrum of issues concerning discipline and governance as well as matters of faith and morals. But that which we call heresy by any other name would smell as rank. - The Grammar of Dissent
Thus not only are dissenters to be known as heretics, they are quite often known as Cafeteria Catholics.
A Cafeteria Catholic is a Catholic who dissents from the doctrinal or moral teachings of the Catholic Church, including those who choose not to receive one or more of the seven sacraments (for example thinking confession to a priest is not necessary to have sins forgiven), and not to follow Catholic teachings on sexual morality, abortion, birth control, divorce, premarital sex, masturbation, pornography, prostitution and homosexual acts. - Cafeteria Catholicism
Heresy within the Catholic Church has very specific delineations. To begin, heresy requires 'public' and 'obstinate' denial of 'doctrinal imperatives'.
Next, the Church delineates between formal heresy and material heresy. As a priest, it could be possible that his opinions about homosexuality and transgender issues come from a 'good faith' error in judgement and, therefore, he might not be acting as a heretic at all. AND: even if it was still heresy, being guilty of material heresy does not count as a sin.
It is even more complicated still. The Church makes a distinction between manifest, occult, public or private heretics. And each of these can be further weighted by four degrees of severity between 'pertinacious adhesion' to 'heretical savoring'.
So, it is clear that any casual observers outside the Church aren't at all qualified to make any declarations about whether certain opinions or beliefs qualify as heresy. It would make more sense to call them dissenters, as this is a term without an official definition in Church doctrine.
If one looks at the Church's actions regarding actual incidents of priests or other Church officials breaking with Church teachings on homosexuality, you will get a mixed bag that includes more or less tolerance depending on each case. I'm not aware of any contemporary case in which anyone was declared a heretic based on their opinions on these matters.
The other answers here are making the church out to be more intolerant than it is.
van Noort, Gerardus Cornelis (1959) . "Chapter II – Article I". Dogmatic Theology. Vol. 2: Christ's Church. Translated by Castelot, John Joseph; Murphy, William Robert. Westminster, Maryland: The Newman Press. p. 237. "The generic terms of the proposition [Members of the Church are all and only those who have received the sacrament of baptism, and are not separated from the unity af the profession of the faith, or from hierarchial unity.] (particularly the second part of it) cover a variety of categories of people: 'formal' and 'material' heretics: 'public' and 'occult'—heretics; 'formal' and 'material' schismatics; 'total' and 'partial' excommunicates; etc. Since the theologians are not all of one mind in discussing some of these categories, they differ in some of the theological labels they append to each category considered singly."