Another update on the off-chance that someone is reading this. I did an IP check through Cloud Shell directly from the VM, and it gives me a different IP address than GCP’s “external IP.” Whitelisting this new IP allows me to connect. Woohoo. (I’m curious why this is the case, but just happy it is finally working.)
However, I still cannot access either the GCP VM stated external IP address (‘cannot connect’ error) or the Cloud Shell reported IP address (‘took too long to connect’ error) through Chrome. I can connect through GCP’s Web Preview, though.