They are, but they’re completely optional and you don’t need to make any purchases to progress through the entirety of the game content. Plenty of people are pure F2P players.

Star Rail and Genshin are both gacha games that are completely enjoyable as a pure F2P player. The main cast of characters plus a few of the easily obtainable F2P characters are more than enough to get you through all of the story and event content, and they even give you enough of a trickle of jades/primogems through free story and event quest rewards that you can pull a few 5* characters (though you obviously have to be a lot more selective on who you want to pull for than a paid player would have to be).