It is a fact and a problem that so many types of modern Christianity are unmasculine: it is a problem for men, and for women.
I won't go into detail - but a lot of what goes on in and around church, and how it goes on, does strike masculine men as effete, and therefore either uninteresting or actively-repulsive.
This is not, of course, a core attribute of Christianity - if Christianity really were intrinsically unmasculine then it could not have survived and thrived for so many centuries; and if Christianity were fundamentally unmasculine then it would be very popular among Leftists, instead of loathed.
(It is, of course, the residual masculine aspects of mainstream Christianity which Leftists most vehemently attack.)
The most fully masculine form of Christianity seems to me to be the Orthodox - and this presumably derives from the style and lifestyle of the majority of priests: stereotypically being large, bearded, deep-voiced patriarchs who dress massively and imposingly.
This makes for a big contrast between the Western and Eastern Christianity which I find very obvious between otherwise-similar countries such as Spain and Greece.
In the West, evangelical Protestants (and Mormons) are among the most masculine of Christian churches, and more masculine than most other modern social institutions - but mostly lack the advantages of a distinctive (and impressive) 'uniform' and a standard liturgy with formal ritual, language and music.
But effete Christian churches are much more significant than style or lifestyle.
The fact that Christianity does not appeal much to masculine men is a criticism and severe weakness of the Christian churches, and a measure of how far they have been corrupted by modernity.
It is also, and primarily, a criticism of masculine men. They need the church, whether it is masculine or not! And there is no doubt whatsoever, that if even a few joined a church and participated actively, then soon it would be more masculine.
Of course, men have also been attracted-out from churches by Leftism, especially with its inducements of sexual and lifestyle license ('sex and drugs and rock and roll'); an ideology which equates masculinity with impulsive self-indulgence.
But such hedonists are easily overcome by religious, disciplined and self-denying men, united by a higher goal.
If a Christian church or denomination can assemble and organise such men - and any such success would be very obvious - it may yet be a formidable and constructive social force.
Note added: A comment from Thrasymachus (below) recommended this useful book:
which gives data to suggest the problem is restricted to Western (not Eastern Orthodox) Christianity and dates from about 1200 - which I interpret as suggesting that 1. the unmasculinity of Christianity is ultimately a consequence of the Great Schism (which I take as the start of modernity), and 2. that a probable cause was the movement leading to enforcement of priestly celibacy in the Roman Catholic church, but that having begun the trend was reinforced by other factors - which spanned the Reformation.
I found particularly interesting the idea that the masculinity of Christianity is apparently related to the understanding life as Unseen or Spiritual warfare - and to the martyrs and ascetic monks as quasi-military heroes.