It turns out they were not that many after all. These networks seem to cover the whole range
66.102.6.0/23
66.102.8.0/23
108.177.64.0/20
66.249.80.0/21
66.249.88.0/22
66.249.92.0/23
Same for Amazon Alexa:EDIT: The following only works for the app. The Echo Dot does not work.
3.248.0.0/13
34.192.0.0/10
52.192.0.0/12
52.208.0.0/13
52.216.0.0/14
52.220.0.0/15
52.222.0.0/16
176.34.0.0/16
54.64.0.0/11
54.224.0.0/11
I'll set up firewall monitoring anyway and check in a month or so if there is any blocked IP address that resolves to amazonaws.com or google.com
3.248.0.0/13
34.192.0.0/10
52.192.0.0/12
52.208.0.0/13
52.216.0.0/14
52.220.0.0/15
52.222.0.0/16
176.34.0.0/16
54.64.0.0/11
54.224.0.0/11