There is a new major release of the ESP8266 core, taking the latest version from 2.7.4 to 3.0.0
There’s a long list of changes, some of which seem quite minor and some that are significant changes. There seems to be a major change to the way that memory is handled, and a number of changes to the WiFi code as well.
The new ESP8266 core v3.0.0 introduces many breaking changes. You even can’t compile your code in certain cases.
The most important breaking changes, which can affect everybody, are in
WiFi : especially when you’re using AP mode, with custom AP IP (such as 192.168.100.1), not the standard 192.168.4.1
SSL: The total deletion of deprecated axTLS will cause the ESP8266 SSL-related Blynk code not compiled. You have to drastically change the code to use BearSSL and update CA Certs. For Blynk cloud server, you can use inSecured mode.
ISR-related code: To use IRAM_ATTR in place of ICACHE_RAM_ATTR