@Pierre:
Removing these files and directories will remove both CyberGraphX and Picasso96:
ENVARC:CyberGraphX
ENVARC:cybergraphics
ENVARC:Picasso96
ENVARC:Sys/screenmode.prefs
SYS:Prefs/Presets/monitors
LIBS:cgxsystem.library
LIBS:cgxvideo.library
LIBS:cgxbootpic.library
LIBS:cybergraphics.library
LIBS:cyberintuition.library
LIBS:cyberlayers.library
LIBS:vilintuisup.library
LIBS:Picasso96
SYS:Prefs/CGXMode
SYS:Prefs/CGXMode.info
SYS:Prefs/CyberGraphX
SYS:Prefs/CyberGraphX.info
SYS:Prefs/Picasso96Mode
SYS:Prefs/Picasso96Mode.info
SYS:Prefs/PVS
SYS:Prefs/PVS.info
Not all files/directories will exist in your system, but just keep going through the list from start to end.
Also, in SYS:Devs/Monitors you need to remove a file which is called something like CyberVision64, CV64, CVision64, Picasso96, P96. When you find it, also remove its .info file.
A reboot afterwards is required.
Btw, in which way cant you switch resolutions? Sometimes bad software will make it impossible for workbench to change resolution (it cant close the screen). The only way then is to select a resolution, save and then reboot. You will then have the new resolition at next boot. Try disabling everything in your WBStartup and User-Startup and then see if you can switch resolutions then.
/Patrik