Icons are not being displayed correctly

I can change basically any section from Tweaks → Appearance → Themes properly, except for the Icons, which doesn't seem to be applied for most of the options.

Here's my Home folder using Yaru for icons:

Here's my Home folder using Humanity, Humanity-Dark, LoginIcons and a couple more. Same output for all of them.

When I try to use alternative themes, such as Dracula, Nordic, Arc-Darkest and Material-Black-Frost, the output is the same. It looks like some kind of system default. Adwaita (marked as default), DMZ-Black and DMZ-White, which are native on my OS, also look the same. This is how they look:

Here is some useful info:

• My GNOME version is 3.38.5.

  ~: cat /usr/share/gnome/gnome-version.xml
  <?xml version="1.0"?>
  <gnome-version>
   <platform>3</platform>
   <minor>38</minor>
   <micro>5</micro>
   <distributor>Ubuntu</distributor>
   <!--<date></date>-->
  

• My GTK version is 3.24.25.

  ~: dpkg -l libgtk2.0-0 libgtk-3-0
  Desired=Unknown/Install/Remove/Purge/Hold
  | Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend
  |/ Err?=(none)/Reinst-required (Status,Err: uppercase=bad)
  ||/ Name              Version            Architecture Description
  +++-=================-==================-============-==================================================
  ii  libgtk-3-0:amd64  3.24.25-1ubuntu4.1 amd64        GTK graphical user interface library
  ii  libgtk2.0-0:amd64 2.24.33-1ubuntu2   amd64        GTK graphical user interface library - old version
  

• The OS is Ubuntu 21.04.

• I tried logging in, logging out and even restarting.

• I got the non-native themes from Gnome-look.

• Icons are stored in ~/.icons and themes in ~/.themes.

• gnome-tweaks version is 3.34.0.

• I use 1920x1080 resolution, even though the native resolution from my hardware is 1366x768. The issue happens in both cases.

• No message is provided when I change icons.

You need to install the Adwaita icon theme. (This is because the full Adwaita icon theme is not included in the default Ubuntu installation).

sudo apt install --no-install-recommends adwaita-icon-theme-full