According to one review -Since there are no manual saves, you have to play the game all over again to get the three endings. There is a pivotal point to get each ending.
At least we got NG+ so another playthrough is easier.
Eurogamer 4/5 - https://www.eurogamer.net/stellar-blade-review
There are three different endings and each ending has its own unique final boss.
German magazines/websites
Gamestar 85
Gamers Global 8.5
GamePro 82
4players.de 84
play3 8.5