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).