Google is not perfect at distinguishing which queries for the word "Go" are actually about the Go programming language.
Referring to the language as golang is a secondary name, popularity driven by Google's own performance surfacing go (language) related results for the word go.
Go (programming language) has the same january drop as golang, clearer when both are viewed together:
https://trends.google.com/trends/explore?date=all&geo=US&q=g...
I don't think Go actually is substantially less popular in Febuary 2021 than November 2021 (January/December, maybe due to people/student vacation time), but the google trends anomaly is not a go vs golang naming distinction.
https://trends.google.com/trends/explore?q=golang&date=all&g...