Just like the Trophy list of Marvel's Spider-Man: Miles Morales, it looks like the Demon's Souls Platinum Trophy is a fairly realistic goal. There's the general difficulty to get around, of course, but this appears to be a fairly straightforward list of trinkets to unlock in your quest for 100%. Exophase has the full list, which consists of 36 Trophies and then the Platinum itself.
You will unlock Bronze Trophies for beating each and every boss in the game, two Silver trinkets for helping another player beat a boss and then invading someone else's game to kill them, as well as Gold Trophies for finding all the Spells, Miracles, and Rings in the game. You can also unlock further Trophies for fulfilling certain requirements alongside slaying certain baddies. Multiple playthroughs will be required, however.
Will you be targeting the Demon's Souls PS5 Platinum Trophy? Start planning your approach in the comments below.