Added

• Add Linux ARM 64-bit support to build system (#2078)
• Expose Arduino state to VS Code extensions (#2110)
• Add advanced setting for moving Serial Monitor to the right panel (#2102)
• Add 中文(繁體) ("Chinese (Traditional)") localization (#2151)
• Indicate submenu containing selected board Tools > Board menu (#2035)
• Add "Light High Contrast" theme (#2027)

Changed

• build: use execFileSync for npm scripts (33ab2a6)
• build: use execa for the packager (36e2092)
• Adjust release procedure and CI system for "trunk-based" development strategy (#2120, #2177)
• Update Theia framework to 1.39.0 (#2027, #2144)
• Bundle application using webpack (#2144)
• Simplify board and port handling (#2165)
• Bump Arduino Firmware Uploader dependency to 2.4.0 (#2165, #2186)
• Generalize name of "Firmware Updater" (#2176)
• Bump Arduino CLI dependency to 0.34.0 (#2121, #2126, #2178, #2186)
• Update translation files (#2031, #2027, #2144)

Removed

• Drop support for MKR 1000 WiFi/WiFi101 and MKR Vidor 4000 from "Firmware Uploader" and "Upload SSL Root Certificates" features (#2176)

Fixed

• Correct order of displayed sentence and paragraph text in Library Manager (#2026)
• Avoid unnecessary GET /sketches request (#1849)
• Enable error diagnostics for sketches in Cloud sketchbook (#669)
• Fix failure of "Save As.." operation when sketch path contains certain characters (#2043)
• Remove non-functional language server-related items from editor context menu (#1394)
• Fix light coloration of title bar when using dark theme (#321, #2125)
• Fix truncation of sketch content when file exceeds 64 kB (#2086)
• Show notification if installation via Boards Manager or Library Manager fails (#621)
• Fix silent failure of save when sketch out of sync with file system (#2051)
• Fix unavailability of language server-based features when sketch stored on different drive from system temp folder (#2034)
• Allow recovery of all types of soft bricked native USB boards (#2089)
• Fix sketch save failure when offline (#2079)
• Warn user when IDE is unable to save the sketch (#2081)
• Include all log args in the log message (#2101)
• Correctly handle presence of multiple supported boards in Firmware Updater and Certificate Uploader UI (#2158)
• Fix unexpected port selection loss during upload to certain boards (#43, #82, #1366)
• Fix unexpected board+port selection change when board is disconnected (#2143)
• Fix hang on startup when attempting to restore sketch from previous session fails with unusual error (#2166)
• Do not start obsolete daemon watcher process (#2182)
• Fix lack of response to first click on "New Tab" menu item (#2183)
• Fix missing app icon for AppImage on Linux (#2190)

Security

• Remove unsafe use of innerHTML (#2064)
• Remove unsafe/fragile use of shell option in process spawning code (#2067, #2112)

Thanks to everyone who's helping us improve the quality of Arduino IDE:

• @nmzaheer
• @streak324

Full Changelog: 2.1.1...2.2.0