OK, there are multiple error reports in Flamerobin trackers about this and no solution in more than 1.5 years. Flamerobin 9.2 works as expected, although it does not support internal functions, but such feature is not necesary for script execution. Apparently, Flamerobin is ceasing to exist.

DBveaver can be good replacement, but it has different convention for scripts, e.g., it does not support multiple commit work; statements in the script.