Problems trying to return to using konqueror as file manager

A while ago, I switched from using konqueror to dolphin as a file manager, because of intermittent konqueror crashes in very large directories (having been using konqueror since before it was konqueror!), but I’d like to return to konqueror as there as some features of dolphin’s behaviour that are to me rather irritating.

However, if I just right click on a directory in dolphin and select open with → konqueror, a konqueror window is opened, and then the directory is opened in a new dolphin window.

Changing the preferences to move konqueror above dolphin in the list has even more undesirable consequences. After doing that, open with → konqueror or specifying a directory in krunner results in an endless(?) stream of empty konqueror windows being opened. The only way I have found to stop it is to go to a console and log in there and issue a killall konqueror command.

On another machine (where I never made the switch as the lack of directories with many hundreds of files meant that I was not having problems with konqueror crashing) konqueror still works quite happily as a file manager. I’m therefore guessing that there is a configuration that has got changed by using dolphin, but so far I’ve been unable to identify it. (The konqueror file management settings look to be the same on both machines).

Does anybody have any suggestions?

Versions:
Konqueror: 20.12.3
KDE Plasma Version: 5.21.3
KDE Frameworks Version: 5.80.0
Qt Version: 5.15.2
Kernel Version: 5.11.6-1-MANJARO
OS Type: 64-bit
Graphics Platform: X11
Processors: 6 × AMD Phenom™ II X6 1055T Processor
Memory: 15.4 GiB of RAM
Graphics Processor: AMD RS880

I think I have identified the problem.
On this one machine, the Embedding setting for directories in Applications → File associations had been set to Show file in a separate viewer rather than Show file in an embedded viewer.

P.S. Konqueror still crashes on very large directories.