Thank you. Indeed, I've tried all of these.
gdb is installed.
I can run the program using /usr/bin/gdb from the build window or from a shell outside of SE. Commanding "start" goes where I expect in the program.
I tried using the SE version of gdb. It has the same result. Here's the log.
chuck@cu20:~/.slickedit$ cat 26.0.0/logs/debug.log
debug[2021-12-06T11:02:10Z]Connected to 'vsdebugio' process on port 26
debug[2021-12-06T11:02:10Z]Connected to 'vsdebugio' process using tty /dev/pts/2
debug[2021-12-06T11:02:10Z]GDB starting gdb: /home/chuck/slickedit-pro2021/bin/gdb
debug[2021-12-06T11:02:10Z]GDB startup arg[0]=/home/chuck/slickedit-pro2021/bin/gdb
debug[2021-12-06T11:02:10Z]GDB startup arg[1]=-nx
debug[2021-12-06T11:02:10Z]GDB startup arg[2]=-interpreter=mi
debug[2021-12-06T11:02:10Z]GDB startup arg[3]=-quiet
debug[2021-12-06T11:02:10Z]GDB startup arg[4]=-data-directory=/home/chuck/slickedit-pro2021/toolconfig/vsdebug/
debug[2021-12-06T11:02:10Z]GDB connect, pid=89308
debug[2021-12-06T11:02:10Z]GDB connect, alive=1
debug[2021-12-06T11:02:10Z]GDB setting PYTHONHOME: /home/chuck/slickedit-pro2021/bin/python2.7
debug[2021-12-06T11:02:10Z]======================================
debug[2021-12-06T11:02:10Z] GDB command_reply: command=-inferior-tty-set /dev/pts/2
debug[2021-12-06T11:02:10Z] GDB command_reply: timeout=0
debug[2021-12-06T11:02:10Z] GDB event: error reading next event -5702
debug[2021-12-06T11:02:10Z]GDB command_reply: error reading events, status=-5702
debug[2021-12-06T11:02:10Z]GDB connect: could not open tty, status=-5702
debug[2021-12-06T11:02:10Z]======================================
debug[2021-12-06T11:02:10Z] GDB command_reply: command=-list-features
debug[2021-12-06T11:02:10Z] GDB command_reply: timeout=0
debug[2021-12-06T11:02:10Z] GDB event: error reading next event -5702
debug[2021-12-06T11:02:10Z]GDB command_reply: error reading events, status=-5702
debug[2021-12-06T11:02:10Z]GDB event parser: Reply did not begin with ^ :
debug[2021-12-06T11:02:10Z]======================================
debug[2021-12-06T11:02:10Z] GDB command_reply: command=-gdb-set auto-load off
debug[2021-12-06T11:02:10Z] GDB command_reply: timeout=0
debug[2021-12-06T11:02:10Z] GDB event: error reading next event -5702
debug[2021-12-06T11:02:10Z]GDB command_reply: error reading events, status=-5702
debug[2021-12-06T11:02:10Z]======================================
debug[2021-12-06T11:02:10Z] GDB command_reply: command=-environment-path -r /home/chuck/4193-controller-ui/douglas/package/controller-ui/build/ /usr/local/sbin /usr/local/bin /usr/sbin /usr/bin /sbin /bin /usr/games /usr/local/games /snap/bin /home/chuck/slickedit-pro2021/bin/
debug[2021-12-06T11:02:10Z] GDB command_reply: timeout=0
debug[2021-12-06T11:02:10Z] GDB event: error reading next event -5702
debug[2021-12-06T11:02:10Z]GDB command_reply: error reading events, status=-5702
debug[2021-12-06T11:02:10Z]======================================
debug[2021-12-06T11:02:10Z] GDB command_reply: command=-environment-cd /home/chuck/4193-controller-ui/douglas/package/controller-ui/build
debug[2021-12-06T11:02:10Z] GDB command_reply: timeout=0
debug[2021-12-06T11:02:10Z] GDB event: error reading next event -5702
debug[2021-12-06T11:02:10Z]GDB command_reply: error reading events, status=-5702
debug[2021-12-06T11:02:10Z]======================================
debug[2021-12-06T11:02:10Z] GDB command_reply: command=-file-exec-and-symbols /home/chuck/4193-controller-ui/douglas/package/controller-ui/build/controller-ui
debug[2021-12-06T11:02:10Z] GDB command_reply: timeout=0
debug[2021-12-06T11:02:10Z] GDB event: error reading next event -5702
debug[2021-12-06T11:02:10Z]GDB command_reply: error reading events, status=-5702
debug[2021-12-06T11:02:10Z]stopping 'vsdebugio' process