imessage sends messages as SMS in groupchat ever since updating to IOS 18

My phone updated to IOS 18 and it was literally the worst experience ever. I can no longer text in my most used group chat now because my messages from my phone only send as SMS and no one else received them. This is supper frustrating and I’ve tried everything to fix it from toggling imessage on and off in the settings and removing my number and adding it back again. Nothing has worked. I’m super frustrated in Apple and wish i never updated. Please fix this asap so many people have had this issue I can’t believe apple hasn’t come up with a fix yet.