You could try Dolphin. It’s the default file manager in KDE, but I think you can install it by itself.

It should be available as an apt package in Ubuntu.

If you’re coming from windows, I think kde may be easier to transition to than gnome.

pcmanfm is a good one

Nemo should be enough for your purposes, and probably looks better on GNOME than Dolphin

I use nemo, its the only one with all the functions I need

I have the same complaint and I dont know either. You can add at least 5 favorite/bookmarked folders that show underneath, but thats all I know of.

Welcome to Gnome. “The defaults are good so you don’t need customization” seems to he their montra. Honestly there probably is a way to change the sidebar however you like, but it will he buried in a config file and break between upgrades. Dolphin might be a better fit. KDE seems to go the other way, not great defaults, but you can customize as you want.

I second nemo. Gnome makes it annoying to swap file managers since you need nautilus installed for the desktop icons so you can’t just remove it. Nemo has its own but they aren’t as good on gnome.

To swap away from nautilus after installing (any file manager, but in this example) nemo you use xdg-mime:

xdg-mime default nemo.desktop inode/directory application/x-gnome-saved-search

And if you use firefox, you also need to change this file:

/usr/share/dbus-1/services/org.freedesktop.FileManager1.service

To point to the new file manager; e.g.:

[D-BUS Service]
Name=org.freedesktop.FileManager1
Exec=/usr/bin/nemo --gapplication-service

By default it is /usr/bin/nautilus or /bin/nautilus.

This is done since firefox does not use xdg to figure out your default file manager (depending on where you got it from YMMV).