Is there a difference nowadays between DRGs and “small attack groups” that pass the defences, accumulate, and occupy the area? I mean I understand the theoretical difference, but is there a practical difference on today’s battlefield in Ukraine?
There are raids intended to cause damage, and attacks intended to secure ground. DRGs often don't take positions they can hold, and often aren't supported with the kind of effort that attacks are. You can't just take a patch of ground and sit there. You need supplies, troop rotations, and support. And you need routes that make it possible to do all of this. DRGs can often penetrate much further largely because they only need to get through once, do their job and find a way back, possibly not even the same route. It's possible to have an area where you can't keep permanent presence because they will get hit by the enemy, but you can pass through now and then, if you're careful, and don't make a habit of it. So I believe we do need to distinguish penetrations by recon and SpN elements separate from firm advances intended to gain ground.
That having been said, your point is taken, one might very well convert into the other. In fact if enough DRGs can go in frequently enough and cause enough problems for Ukraine, it's possible they will force Ukraine to pull back from any area where they have a hard time maintaining a stable front line, and thus allow for a Russian advance to take place. But the frequency of this seems to be awfully high, which is why I allow for a different possibility, namely that actually a substantial Russian element has penetrated Ukrainian lines and is now in the process of establishing themselves, and the result could be the loss of a substantial part of Pokrovsk without a traditional large scale assault. There is even a third possibility, that Ukraine is already pulling out of the area, but not yet willing to admit this publicly, and the Russian penetrations aren't of any sort of solid Ukrainian presence, but rather of Ukraine's rear screening elements as they pull out their main forces.
Russian forces north of the conurbation are continuing to advance, so it's starting to look like that "eastern" (now northern) pincer will complete the envelopment to the point where logistics will be compromised and Ukraine will have to do a withdrawal under drone controlled roads, like they had to in previous cases, unless they're already pulling out. On the northern side the second refuse mound seems to be next in line for assault. There are also, so far, unconfirmed reports of similar Russian recon team penetrations into Mirnograd from the north-east.