Sometimes it's a little bit of a futile task to identify plants by a single picture of leaf closeup only, but in this case, it really looked familiar like a weed I have seen somewhere in my yard.... (Where have I seen those innocent looking leaves before???)
Using the very cool U of Wisconsin weed identifier, it looks a lot like Epilobium ciliatum. According to internet, it grows in lots of different places in the world, and sometimes called Willow-herb. Looking it up, I don't find any horrendous characteristics of this weed - like toxicity or extreme invasiveness, etc. But it does make those fluffy parachute-type seeds that float on the wind, so I guess that could be sort of negative.
I don't know if this is your plant, but if nobody else comes up with a better match, maybe look this one up & see what you think.
photo from https://oregonstate.edu/dept/nursery-weeds/weedspeciespage/nwh/nwh_foliage.html