How is tolerance to the kuffar to be done beside doing nahi munkar. I mean like we should let the christians do their worship (without helping them in any way), but isnt seeing that they worship something beside Allah (like they do their rituals outside the church so i can see it, or in the church but not inside the building) oblige us to forbid evil?.

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

There is no contradiction between showing tolerance towards the disbelievers and forbidding them from doing what is evil.

Showing tolerance towards the disbelievers means refraining from wronging them or assaulting their properties and honor, but it does not mean abstaining from inviting them to the truth and forbidding them from doing what is wrong.

Muslims forbid one another from doing what is wrong and enjoin one another to do what is good, but this does not mean that they are not tolerant towards each other.

As for the disbelievers living in Muslim countries, they are not allowed to manifest evil practices or perform the rituals of their religion publicly. They should be forbidden from that as entailed by the Thimmah contract and the covenant between us (Muslims) and them. It is stated in Khashshaaf Al-Qinaa‘ ‘an Matn Al-Iqnaa‘:

They should be prevented from manifesting evil acts like incest, and from publicly ringing their church bells, reciting their religious book out loud, raising their voice while mourning their dead, manifesting their religious festivals, or displaying the cross. This is because the terms of the Thimmah contract, as reported by Ibn Ghanm, included: “And we shall not ring a bell except lightly inside our churches without displaying (a cross on) them. We shall not raise our voices in the prayer or when reciting in our churches in the presence of Muslims. We shall not display our crosses or our books in the markets of the Muslims, nor shall we display (manifestations of) Shirk (associating partners with Allah).” He (Ibn Muflih ) said in Al-Mubdi‘: “Thus, it becomes clear that they are not allowed to manifest any of the symbols of their religion in Muslim lands, neither when praying for rain, nor when meeting kings, nor during any other event, and this opinion was held by Shaykh Ibn At-Taymiyyah.” [End of quote]

As for performing their religious rituals without demonstrating them, such as performing them in the privacy of their churches, homes, or the like, then they are entitled to that, and they should not be prevented nor forbidden from it.

Allah Knows best.