How can I write a program to press keys, such as Windows + D, in Wayland? (replace `xdotool` in Wayland)

I figured it out. Thank you very much to @Rinzwind for pointing out the existence of ydotool!

Here's how to have ydotool press Windows + D. It works in both X11 and Wayland!

I first wrote about this on my website here: Tutorial: Getting started with ydotool to automate key presses (or mouse movements) in Linux.

For full details, see my article. Here are the key parts, copied directly from my article above:

First, build and install it:

# install dependencies
sudo apt update
sudo apt install git cmake scdoc

# build ydotool
# See: https://github.com/ReimuNotMoe/ydotool#build
git clone https://github.com/ReimuNotMoe/ydotool.git
cd ydotool
mkdir build
cd build
cmake ..                 # takes < 1 second
time make -j "$(nproc)"  # takes < 1 second
sudo make install
# Note: the install command installs here:
#
#       -- Install configuration: ""
#       -- Installing: /usr/local/bin/ydotoold
#       -- Installing: /usr/local/bin/ydotool
#       -- Installing: /usr/lib/systemd/user/ydotool.service
#       -- Installing: /usr/local/share/man/man1/ydotool.1
#       -- Installing: /usr/local/share/man/man8/ydotoold.8

# See the man pages for help, and to prove to yourself it is installed
man ydotool   # for the main program
man ydotoold  # for the background daemon process
# help menu
ydotool -h    # for the main program
ydotoold -h   # for the background daemon process [VERY HELPFUL MENU!]

# check the version; my output is `v1.0.4-0-g57ba7d0`
ydotoold --version

Now, use it: have ydotool press Windows + D

# 1. start the `ydotoold` background daemon (`sudo -b` runs it in the
# background; see `sudo -h`).
# - It takes a couple seconds to fully start up and print "READY". Once it does
#   that, hit Enter a couple times to clear out the command line.
sudo -b ydotoold --socket-path="$HOME/.ydotool_socket" --socket-own="$(id -u):$(id -g)"

# 2. Use `ydotool`
# - Have ydotool press Windows + D once to hide all windows, then make it wait 2
#   seconds, then have it press Windows + D again to show all windows:
YDOTOOL_SOCKET="$HOME/.ydotool_socket" ydotool key 125:1 32:1 32:0 125:0; \
    sleep 2; \
    YDOTOOL_SOCKET="$HOME/.ydotool_socket" ydotool key 125:1 32:1 32:0 125:0

# 3. Additional commands you may need: to show, kill, and help

# See the `ydotoold` background running processes
ps auxf | grep ydotoold

# Kill the `ydotoold` background running processes
sudo pkill ydotoold

# View the `ydotool` main help menu, including a list of all sub-commands.
ydotool -h

# View the `ydotool` sub-command help menus. 
# - Bug ( https://github.com/ReimuNotMoe/ydotool/issues/206 ): the daemon *must*
#   be running first to see these help menus!
YDOTOOL_SOCKET="$HOME/.ydotool_socket" ydotool key -h
YDOTOOL_SOCKET="$HOME/.ydotool_socket" ydotool click -h
YDOTOOL_SOCKET="$HOME/.ydotool_socket" ydotool mousemove -h
# etc. 

# Open the Linux C header file containing all available key codes that `ydotool`
# can press
gedit /usr/include/linux/input-event-codes.h

You can also see all possible key codes in this file online: https://github.com/torvalds/linux/blob/master/include/uapi/linux/input-event-codes.h.

Again, for more details, see my website: Tutorial: Getting started with ydotool to automate key presses (or mouse movements) in Linux.

See also

1. How can I add "Show desktop" to the GNOME dash or Ubuntu Dock?
   1. @AndAC's excellent wmctrl answer
   2. my spin on the wmctrl answer, relying on my eRCaGuy_dotfiles repo I have with scripts in it.
2. Q&A: How can I install the latest ydotool 1.0.1 (keyboard automation tool working on Wayland) in Ubuntu 22.04?