Teensyduino 1.56 has been released << Release change note here
pjrc.com/teensy/td_download.html
Quick summary: 1.56 brings support for Arduino 1.8.19 and many fixes and improvements. Teensy 4.0, 4.1, MicroMod get a bootloader update which allows LittleFS_Program filesystem to persist across code uploads.
IDE 1.8.19 supported is the same since 1.8.16 but: "Removed log4j from IDE"
Code:
Arduino Software Release Notes
ARDUINO 1.8.19 2021.12.20 SECURITY HOTFIX RELEASE
* Removed log4j from IDE. Fix CVE-2021-45105, CVE-2021-45046
* Upgrade log4j to 2.16.0 - Extra hardening for CVE-2021-44228
* Upgrade log4j to 2.15.0 - CVE-2021-44228 (thanks @rhowe)