This is a Google design mandate. You will find the same behavior on all Android phones. BTW, your notifications were *always* grouped by app, particularly messaging apps because people usually get many and it's easier and neater to group them than have them scattered, and more people prefer it that way than don't. It's just that now, they are stacked instead of just having the first three notifications visible in a single box with a little expansion arrow with the number of notifications to the right. The new stacks not only show the number of notifications in the stack, but are much easier to break apart without dismissing the whole stack. If you want to see all your notifications unstacked, just tap the stack and they will separate, or download and utilize Good Lock's NotiStar on your lock screen (or just view them in the app).
First pic is a grouped reminder notification on Android 13/OneUI5.1. Note, that it is still grouped, but not stacked. Second pic is NotiStar on the lock screen. You can see each notification is separated.
Grouping is not the problem, the problem is that you cannot disable it.
It may be that majority of people like it that way, but at the same time they were used to the old stile only 2 versions before. It is just cheaper to support one feature instead of two.
I also have old pixel 6 pro with android 16 and it does the grouping much better. While the notification are still grouped it show the text from multiple notifications. They are grouped in the single balloon for every app, but still you can see multiple messages from that app without extending the balloon.
In Samsung you can see only last one which is unsatisfactory.
This screenshot if from pixel
on samsung you will see only the last one
