migration freeze
The mouse freezes on the new iMac at end of migration summary, saying Flash player incompatible. Old iMac is ok.
Flash has been dead over a year, you should have uninstalled it per Adobe.com's instruction ages ago.
Please advise how you are migrating in detail, are you using Wi-Fi, ethernet, Time Machine from the old Mac, carrier pigeon :-) or what. The more information we have the easier it is to help you out.