If you're saying everything works fine with local files, but just not remote ones, then it's a mime types problem.

Have a look and see if this is useful: https://www.reddit.com/r/kde/comments/1bd313p/dolphin_not_recognizing_file_associations/

If not, there's another angle to attack.

install KIO packages if tou do t have them dolphin needs these for network shares to behave like local files:

sudo apt install kio-fuse kio-extras ffmpegthumbs

then log out and log back in (or restart)

dolphin should mount network paths under

/run/user/your-uid/kio-fuse-somerandomshit

check it

if the path starts with /run/user/… you’re good. If it’s something like smb://, it’s not using fuse

gpt explainstion for education

What’s going on:

Your server has files. Dolphin can look at them, but it’s not actually pulling them down to your computer in a normal folder.

Because the files aren’t really on your computer, other programs can’t just “open” them — they don’t know how to talk to the server like Dolphin does.

How it should work: If you use FUSE (with kio-fuse), Dolphin secretly makes a fake local folder that pretends the server’s files are on your computer.

Now, when you double-click a file, your computer thinks it’s opening a local file — so any app can work with it.

Why Nemo works but Dolphin doesn’t Nemo automatically mounts network folders in that “pretend local folder” way.

Dolphin can do it too, but only if kio-fuse is installed and working.

Without it, Dolphin is basically just showing you a picture of the files instead of giving them to your apps.

The fix: Install the thing (kio-fuse) that makes the fake local folder.

Restart your session so Dolphin uses it.

Now Dolphin acts like Nemo — server files will just work everywhere.

Mint doesn't even support kde, so at best you would be grabbing it from Ubuntu's repos which is probably out of date. Which leads to the problem of people on fixed release distros reporting problems that have already long since been fixed, so In addition to others suggestions of testing it out on a full plasma installation. I would also recommend testing it out on a distro known to be up to date in the first place.

You might want to load actual KDE to see if this is a real bug of Dolphin, or if it doesn't work properly because you're running it via Cinnamon. KDE apps are very integrated to the rest of KDE, and some stuff need to run in order for them to work properly. So you can't always depend on another DE's integral part (as is a file manager), without the rest of the DE.

You could try installing cifs-utils

Technical if talking they using different backend under hood I mean nemo and dolphin .Dolphin one a bit sucks in my opinion.To make it work better it would better try mount samba share using fstab file