Oh you mean encounters repeatedly spawning in areas, like in DA:I. Okay fair enough. But for me a trash mob fight is any encounter, even a so-called "hand-crafted" encounter, where I have to fight a gazillion enemies just for the heck of it -- which is how I view the goblin camp encounter in BG3. The original BG games also had these, the gnoll stronghold being a great example. But at least there you could just auto-mow through the hordes and be done with it, which I vastly prefer to the tedium of the BG3 goblin camp fight.
I wonder how much of the tedium you experience is down to you having wiped the camp out a gazillion times just for the heck of it. And how much is down to the game still not having implemented a difficulty rating. Larian is still using the EA "death map" metrics to tweak individual encounters, but not all combat scenarios *should* be equally hard or indeed that much of a challenge. Especially given Larian's stubborn love for exploitative/cheesy gameplay mechanics that allow for overly easy wins.
Even so, the tactical turn-based combat of BG3 is VASTLY superior to the RTwP combat in BG1-2 or Pathfinder games in my opinion. RTwP is a relic of a bygone era unless implemented like a Diablo-style click-fest with all trash mobs all the time.
I agree with you about the difficulty levels not yet available in BG3 and how that could make some difference.
But of course I disagree with the last part. TB combat is the older system by far and not RTwP, so it is TB that's a relic of the past. The very act of taking turns to engage in combat makes the system tedious, boring, and unrealistic. In fact I would go even further and classify taking turns for combat as the ultimate expression of cheesiness.
