I've compiled a series of mostly academic sources on dog whistles, these provide a good introduction to the topic of how these dog whistles evolve to avoid detection in order to continue spreading hate content online and in the recruitment of new neonazi or other extremists.
Generally the tactic is to evolve language to use semantically neutral speech with messages encoded that signal to specific subpopulations in order to more easily mask the true intention of the content. This allows them to fly under the radar on social media platforms and continue to spread hate content and minimize bans.
This paper serves as a comprehensive intro to extremist dog whistles online:
White nationalists and dog whistles on twitter:
link.springer.com
Open access:
The development of racist dog whistles during the BLM protests within politics:
Information on LGTBQIA+ related dog whistles:
swu-union.org.uk
More on gender related harm encoded in semantically neutral speech:
link.springer.com
Computational science paper on the identification of novel dog whistles:
Book on Nationalism and Populism and the use of dog whistles in various countries:
Canada specific example of a eugenics dog whistle:
Study showing that claims of antichristian bias can serve as a racial dog whistle:
Generally the tactic is to evolve language to use semantically neutral speech with messages encoded that signal to specific subpopulations in order to more easily mask the true intention of the content. This allows them to fly under the radar on social media platforms and continue to spread hate content and minimize bans.
This paper serves as a comprehensive intro to extremist dog whistles online:
White nationalists and dog whistles on twitter:

Covert Hate Speech: White Nationalists and Dog Whistle Communication on Twitter
Dog whistling, a form of symbolic communication through seemingly innocuous terms is a common practice for members of far-right movements. This chapter examines how dog whistling was used on Twitter during the 2016 presidential election through a virtual ethnographic...

Open access:
The development of racist dog whistles during the BLM protests within politics:
Information on LGTBQIA+ related dog whistles:

Part 4: Dog whistles in context – transphobia - SWU Social Workers Union
jane fae shares her knowledge and perspective of the ongoing issue of transphobic dog whistles in the UK as part of this educational blog series for social workers.

More on gender related harm encoded in semantically neutral speech:

Pronouns, Gender, and Harm
Recent work in linguistics and philosophy extensively explores the way in which speech can harm others. Most of this research focuses on expressions such as slurs which encode harm or derogation in their conventional meanings. But it is also possible to harm and...

Computational science paper on the identification of novel dog whistles:
Book on Nationalism and Populism and the use of dog whistles in various countries:
Canada specific example of a eugenics dog whistle:
Study showing that claims of antichristian bias can serve as a racial dog whistle: