@mamba
In my view, agency in a RPG is about capacity to influence the outcomes of play. In my preferred RPGing, the main outcome is
establishing a shared fiction. In Gygaxian dungeon crawling, the main outcome is
beating the dungeon, which combines puzzle-solving and wargaming.
In either case, the capacity of a player to influence those outcomes depends on the GM being constrained: in the first case, constrained as to how framing and consequences are narrated (these are the core of the fiction that is being created); in the second case, constrained by their prep so that the puzzle and wargame scenario remain constant, thus knowable and thus beatable.
There is a lot more that can be said about how to operationalise these constraints, in each case. But I hope I've set out the essence of them clearly enough.
Simply talking about a player having their PC go "somewhere on the overland map", without getting into the processes of play on both player and GM side which
enable the player to influence the outcome of play, leaves me in a position where I can't say anything meaningful about agency.
What I will say, as I have said many times previously, that I think part of the genius of the
dungeon conceit is that it is an artificially austere environment, with very clear conventions around how its architecture and interior design are relevant to play. Wilderness and urban exploration, with frequently non-austere environments that are not governed by clear conventions, is in my view far harder for a GM to hold constant so as to be gameable in the way that a dungeon is.