When I upload a file, say to this forum, this pops up:
Try,
sudo apt-get purge dolphin
sudo apt-get purge --auto-remove dolphin
In the terminal, If this does not return anything. It means Dolphin is not Installed.
You got some Updates There, Run
sudo apt upgrade
Also Try,
rm ~/.config/dolphinrc
rm -rf ~/.local/share/dolphin
Thunar, File Manager
That's the name? I- wait isn't Thunar something else?
Wait, is Thunar the one that Vivaldi is opening?
Also, in some folders when I click, it says
Did you installed baloo search with Dolphin?
Yes, That's It.
No, I just installed full KDE plasma and stuff with it (I was curious), removed it, reinstalled it to fix something that it broke, and left it there without touching
Try,
balooctl disable
sudo apt install -s dolphin
sudo apt remove --purge libkf5balooengine5
rm -rf .local/share/baloo/
sudo apt install -s dolphin - didn't work yet
sudo apt remove --purge libkf5balooengine5: didn't work yet
Wait, I Found Something.
maybe I'll end up purging KDE? this... is annoying. 'Specially because Thundar is kind of broken. What would you recommend I do?
If we are trying to go towards removing something, I would recommend to remove Vivaldi and switching it with brave. if the Problem Persists you can remove KDE 
To Remove Vivaldi
sudo apt-get --purge remove vivaldi-stable
rm -i -rv ~/.cache/vivaldi ~/.local/lib/vivaldi ~/.config/vivaldi
sudo apt autoremove
To Install Brave
sudo apt install apt-transport-https curl
sudo curl -fsSLo /usr/share/keyrings/brave-browser-archive-keyring.gpg https://brave-browser-apt-release.s3.brave.com/brave-browser-archive-keyring.gpg
echo "deb [signed-by=/usr/share/keyrings/brave-browser-archive-keyring.gpg arch=amd64] https://brave-browser-apt-release.s3.brave.com/ stable main"|sudo tee /etc/apt/sources.list.d/brave-browser-release.list
sudo apt update
sudo apt install brave-browser
I have a very customized vivaldi setup no browser could ever come close to (vertical tabs, no new tab button, web panel, etc.)
I'm going to try purging KDE