For those affected by the blocks, Signal recommends turning on its censorship circumvention feature.
Signal is being blocked in Venezuela and Russia. The app is a popular choice for encrypted messaging and people trying to avoid government censorship, and the blocks appear to be part of a crackdown on internal dissent in both countries.
Without having read the article, I guess it relates to the recent Signal blog post by Meredith Whittaker https://signal.org/blog/proxy-please/