... because the new IDE installs in "C:\Users\<user>\AppData\Local\Programs\Arduino IDE\Arduino IDE.exe." B4R doesn't seem to like the space in the new name. So I copied "Arduino IDE.exe" to Arduino.exe. Now B4R complained about missing arduino_debug.exe, which is indeed not available. Note that the old Arduino IDE (v1.8.13) remains installed in "c:\Program Files (x86)\Arduino\..."