As mentioned, that AVG anti-virus is perniciously present, and may be blocking some aspect of the Kindle application. You need to thorougly remove AVG, and that might be as simple as one of its menu items offering uninstall, or more elaborate steps from the vendor. There are no real viruses to be found on the Mac, just adware and malware which Malwarebytes can handle by itself. The built-in security, read-only system areas, for other reasons, will not allow Windows targeted viruses and trojans to install in Big Sur.
Once you have thoroughly removed AVG anti-virus, reboot your Mac, and re-install the Kindle v1.3.0 application. Any change in behavior? If it croaks again, remove Malwarebytes (its Help menu has an uninstall), reboot the Mac, and reinstall the Kindle v1.3.0 application again. Is it now stable?
You have a great many useless Internet Plug-ins still installed that Safari no longer uses. Silverlight was killed off on the Mac by Microsoft in late 2016. The Adobe Reader PDF plug-in is no longer used by Safari either.
I don't know where you are storing your Kindle books, but suspect may be DropBox or One Drive. Try placing one of the books on your Desktop and see if Kindle v1.3.0 remains stable reading that book.