But having played HI3 will certainly enhance your experience and offer you a deeper and easier understanding of the characters and the nature of the multiverse. So yeah, on a very basic level, no, I don't think you will have to play HI3 to understand the story of HSR. Certainly worth exploring if you're into that. Also, the story in HI3 is one of the best you can find in any anime-related game on the market. Without prior knowledge, these things lose a lot of their value IMO. Or recognizing the fact that Clara has a mini Wotan and how the whole relationship between Bronya and Cocolia mirrors their relationship in HI3. Or seeing Natasha as a calm, sweet doctor. Many people were freaking out because of the relationship between Bronya and Seele. Picking up on those could really enhance your experience. For one, even if the game will not require prior knowledge of HI3 as we saw in CBT1, it's still full of references to HI3. If you don't want to play the game, watch a playthrough on YT. At this time y'all have the time to do so.

Star Rail seems to be many months (maybe even more than a year) away from its release.

My suggestion for anyone interested in Star Rail, especially if they are interested from a lore and story perspective is to play HI3. Since Welt from HI3 is playable in HSR, more characters could also appear in the future.

No one knows what they'll add in the future and how they might tie the games. But, remember, it's CBT1 and it was only a small part of the game. From what we've seen in CBT1, no HI3 knowledge is required to understand the main plot of the first planet. As far as we know, the game seems connected to APHO and Alien Space which are part of the Honkai Impact storyline.

Carole honkai: star rail