I know that the game doesn't have an offline mode, but at the time being I'd prefer playing entirely solo, without seeing or interacting with other player characters. I have disabled the chat, but players running with glamorous gear and pets add a cluttered feel to the hub areas (assuming that others can't join me on quests without an invitation).
The closest thing you can get is Solo Self-Found mode. In this mode you cannot trade or create parties. However, you will still see other SSF players in towns - that's the way game developers earn money - they sell fancy microtransaction items for players to show off.
You can try playing less popular leagues / platforms. I think Normal (non seasonal) Hardcore SSF on consoles will have the smallest number of players.