High Wall of Lothric · From above
Dark Souls Tracker is a free set of precise top-down Dark Souls 3 maps, level by level, with every bonfire, boss and item where it really stands, the Ashes of Ariandel and The Ringed City DLC included. Load your DS30000.sl2 save and the tracker shows which bonfires you have lit, which bosses you have beaten and what you have already picked up, where your character stopped and how to walk to the item you are after.
On Windows: %APPDATA%/DarkSoulsIII/<Steam ID>/DS30000.sl2, in a folder named after your Steam account. On Steam Deck and Linux (Proton) the same folder is inside compatdata/374320.
No. DS30000.sl2 is read in your browser and stays there. When you are signed in, your account keeps your ticks and the spot on the map, and the rating receives the character's build - level, stats and weapons - but never the file itself.
Yes. Both DLC have their own maps with their bonfires, bosses and items: switch the campaign in the side panel.
Yes. The maps, the search and reading your save are free. The maps and the search work without an account; reading your save and ticking by hand need a free one, which also keeps your ticks in step between devices.
Not everything is written into the save. Where the save cannot confirm a marker, the tracker says so, and you can tick it off by hand.
High Wall of Lothric · From above