re-downloaded 4.2.1 Firmware again: Laser does not switch on with “M2233 V1” . More or less awaited, because I expect the uArmStudio does use the same command. With putty the response on this command says: [Check door] !! (… without given request-Id). That underlines this command is not realy adapted to the uArm.
OK another test:
#9 M2400 S1
G1 X10 Y10 Z10 F1000
#10 M2233 V1
with the second sequence the Laser has switched ON - yeah! …means in the IDE the initialisation does work only with the old firmware! Seems (M2233 V1) does switch on - not G1! This is not documented (implemented?) in the old firmware - but now necessary - pure speculation…!
By the way: After closing uArmStudio there are still running uArm processes and the opened uARM-COM port is not released. You have to kill the processes manually in front of putty testing,