Hi, if you use 2.1.1, please get the nightly build: https://www.arduino.cc/en/software#nightly-builds
Previous forum post: Arduino IDE 2.1.0 do not save sketch without internet.
Original GitHub issue: Sketch not saving while Offline · Issue #2079 · arduino/arduino-ide · GitHub.
Here is why you need to use the nightly build: The IDE does not save the sketch when the Internet is off · Issue #2142 · arduino/arduino-ide · GitHub.