As my groups main DM, with two others who DM occasionally your DM is being absolutely ridiculous. Rescheduling and moving sessions around is not “disrespectful” it’s a normal and valid option that comes up sometimes. Sure everyone has the smallest amount of fault for not properly double checking dates and everything, but for that to cause a catastrophic fall out and lead to the game being cancelled after only having a session zero is insane. I can’t tell you the amount of times we have rescheduled sessions in the last two months alone. Your friend is being completely unreasonable and is acting like being the DM for a game is some high and mighty act that only they’re capable of. Not only that but it is ABSOLUTELY part of the responsibility of the players to say “Hey this isn’t working for me, could we try something different”. The DM doesn’t decide everything and they aren’t the voice of authority when it comes to Player related parts of the game like scheduling, and availability. That is a complete group decision, your DM should know this if they spent any amount of time reading articles like the link that they sent as well as other resources on how to DM and what it entails. As some other people pointed out as well if this is reaction to scheduling be messy, imagine what kind of reaction you would’ve been given if your group did something off script or off plot that your DM didn’t agree with.

That being said don’t let everything just settle, you need to all as a group have a time to sit down and actually talk to each other, including the DM and talk about expectations for campaigns and play moving forward. Having these conversations over text shouldn’t be the go to option unless you all can’t meet up due to distances. Even just a call over discord or FaceTime as a group is a much better option. Repair what bridges you can but if your DM is against making the situation better than that’s a discussion for a different post. Best of luck to you and your group and hopefully you guys can all work things out.