In order to get the true ending in Resident Evil 2 Remake you need to do the following:
- Beat the game with either Leon or Claire.
- After the first playthrough you unlock “New Game [2nd Run]” in the Main Menu. Select that mode, it’s the secondary “B” campaign.
- Finish the B-campaign of either character and you will get the True Ending. It doesn’t matter if you play as Leon or Claire.
So in summary, you need to do at least two playthroughs of the game.
Seeing the true ending also unlocks the Broken Umbrella trophy or achievement.