Can't see any of your pictures. When you write back with good links, please mention where you live and what kind of grass you have.

Looks like dallis grass to me, too. If it puts out a v-forked seed stalk, with fairly dark black seeds dangling off of it, you'll know for sure. Check dallis grass out with google images to see. It is tough, but not super difficult to take out. Gather up the leaf blades with one hand to reduce the possibility of leaving segments with roots behind & to find the base of the plant. Get a weedstick & push it into the ground right next to the crown of it (where the root base & the leaves meet). You are using the weedstick both to go around the base, cut the roots & help jimmie the thing up out of the ground. You'll be pushing the weedstick in around the base at various points until it loosens up enough that you can pull it out without straining your muscles or throwing your back out! (Yes, my DH has managed to do that on more than one occasion - don't try to beat it by aggression, lol!) I am puny, but the smaller ones I can get with just one stab & an established patch I simply take out in sections. The only "injury" I've ever suffered from dealing with it is hand fatigue! The good news is that, unlike some obnoxious weeds, if you get dallis grass's white fleshy base out, it does not come back from the roots left behind so it's okay not to dig the whole thing out. If you have a lot of it & have to pace yourself, make the sections developing seed stalks your priority!

This looks like the weed I have been trying to deal with in a garden at my daughter's school--I just thank goodness it's not growing in my own yard (though I do have every other weed possible I think). I hadn't been able to ID it until I saw it here, either this forum or Name That Plant. It's Sheep Sorrel (Rumex acetosella)I believe. Let me know if you figure out a way to get rid of it, please!

Fortunately for you it is not Japanese knotweed. https://slate.com/technology/2019/05/japanese-knotweed-invasive-plants.html