Hi Sean, sorry to hear you are having trouble starting Minecraft. Please see MCL-17030 and attach the launcher log to that bug so we can identify the issue. You can find the instructions in my comment on that bug. Thanks!
Exact same issue as you, I also opened this as an issue since I didn't see your comment. A temporary fix is to delete the assets folder and the launcher will start with download instead of preparing. I only experienced this issue after updating the launcher toady. I'm using Ubuntu.
Hi Sean, sorry to hear you are having trouble starting Minecraft. Please see MCL-17030 and attach the launcher log to that bug so we can identify the issue. You can find the instructions in my comment on that bug. Thanks!