"I still often hear that a successful programmer should be 'puzzle-minded' whereas I have the feeling that a clear and systematic mind is more essential. A modern, competent programmer should not be puzzle-minded, he should not revel in tricks, he should be humble and avoid clever solutions like the plague" ( https://www.cs.utexas.edu/users/EWD/transcriptions/EWD03xx/E... ).
The real problem of cleverness is when people are bored of being code monkeys and start inventing things that complexify their project without any legitimate justification. Like "a cron job and a two line shell script would do but why don't I design my own multi-tier scheduling cluster"
Dijkstra's comment was made when assembly language was widespread, and I suspect that his idea of "clever" involved the various ways people can famously make assembly language unreadable.
In the introduction to "A Discipline of Programming," he asks if advanced language features belong to the solution set or the problem set, but he doesn't define "advanced," so I can't say where he put the threshold.