I have the same problem of Affinity Publisher repeatedly freezing. I am running it on Windows 11 on a desktop computer. I am writing a book - the file is 20 MB. The document is mostly text, but it also includes a lot of small black and white graphics.
Publisher has started freezing in the last two or three days. Previously I could close and re-open the application and it would then work OK, but today it has frozen about three times, and the last two times it froze after I typed about 4 characters.
UPDATE: I have just seen another user's note saying that Affinity strongly recommend not saving on an external drive. I was indeed saving this file on a "Network-Attached Storage" device (I don't know exactly what that means, but the device is connected by a cable to my computer). I therefore made a copy direct from that location to my PC and then opened that copy, and now Affinity Publisher doesn't freeze immediately.
Also, when Affinity opens, it automatically also opens the file I had open last time it closed, a feature I rather like and that had stopped working. So, two problems solved by saving on my PC instead of on an external disk!
SECOND UPDATE: I spoke too soon - the freezing has returned twice already! The application runs for 15 or 20 minutes before freezing, which is better than freezing after typing four letters, but still bad. I have lost all work I had not saved before it froze.