Some problems (Kingdom Come: Deliverance)

Because you're not a monk ?

You've been exposed or repeatedly break the daily routine in the monastery.

SlacherCat
your stay is not legitimate - not the plot, not to wear all sorts of cloths and walk where you want. Through the story you need to obtain a permit for your stay in the monastery.

If penetrated to the monastery, try to remain in the shadows.

SlacherCat wrote:
if I'm wearing a monk's clothes
And it would be interesting if it added points to stealth.

Monks can be defeated by Sanaa cloth, in the CCC, they are not particularly formidable, get them out and live in the monastery itself.
Let them know who is coming!