I mentioned earlier in the thread that GMs, when creating settings and scenarios, should do so with both the fiction and the gameplay in mind.
I suspected this was what you meant, but wanted to be sure since we clearly diverge in certain views. I don't have a neat binary view/approach on this; it varies by game and campaign.
I don't know how familiar you are with V:TM V5, but in case you're not (and for anyone else reading who isn't), Chronicle Tenets are decided by the group before play begins. They establish what is effectively the coterie's shared moral/ethical outlook and as such signal to the GM what the nature of any moral dilemmas the coterie face should be. They are specifically meant to be tested (a not uncommon misunderstanding is treating them as lines and veils). Any character breaking a chronicle tenet gains a "Stain", which can result in loss of humanity (a roll is made at the end of a session to check).
Characters also have their own personal morals/ethics noted by Convictions, which are meant to bind them to their own humanity. These can deviate from or even contradict the Chronicle Tenets, and be used to mitigate Stains from breaking a Tenet if it's done in service to a Conviction. Breaking a Conviction may also incur Stains.
So, if I'm running V5, part of my job as GM is bring scenes to bare that specifically test those Tenets and Convictions - a rule of thumb I use for this is that any moral dilemma should have an easy out by breaking the Tenet/Conviction and sticking to it should pose a problem for the Kindred's unlife. But since I'm specifically curating such scenes as a GM, I consider that less sandbox-y. I also wouldn't being doing this in, say, D&D
Speaking of D&D, I already mentioned I wouldn't run it as a sandbox, preferring a non-linear railroad approach. But something I prefer for D&D is personal questlines similar to what Mercer does in Critical Role, or companion missions in a BioWare game. But what I do for these is take into account the player's abilities or lack thereof. So, I might have enemies or situations that are specifically designed to showcase the focussed PC's strengths, so they can be the big damn hero, but I'll also have others that highlight their weaknesses/deficiencies to show why they need their allies (the other PCs) - and that's done for all PCs so I'm not playing favourites. Ideally, these will also highlight their BIFTs, but not in a way similar to V5. That said, I generally give no consideration to the PCs for the main plotline unless the BBEG learns of them and is cunning enough to factor them into their plans.
Meanwhile, I've recently been pondering a Conan pastiche, possibly using Barbarians of Lemuria or maybe the new Conan game from Monolith, and for that I imagine I wouldn't be factoring in the PCs at all.
If you also extend this to include rules incentives, then I'm at odds with
@robertsconley. XP (or equivalent) being granted for the things you want to see in play is game design 101, as far as I'm concerned. I actually wrote a bunch of XP triggers for my V5 games (the official ones are possibly the worst I've seen).
Does that answer your question?