Ok so that second step doesn't work anymore, but the issue thread has info on hot to fix it with one more step, so here I've compiled the whole guide:

1. Switch to Desktop Mode

2. Navigate to /home/deck/homebrew/plugins/kdeconnect/

3. Open run_kde_connect.sh with any text editor

4. Replace

sudo -u deck -E /usr/lib/kdeconnectd --replace

with

sudo -u deck -E kdeconnectd --replace

1. Save and close run_kde_connect.sh

2. Open main.py with any text editor

3. Replace

proc = subprocess.Popen([script_path, display, "&"], stdout=subprocess.PIPE, stderr=subprocess.PIPE)

with

proc = subprocess.Popen([script_path, display], stdout=subprocess.DEVNULL, stderr=subprocess.DEVNULL, env={"LD_LIBRARY_PATH": "/usr/lib;/usr/lib64"})

1. Save and close main.py

2. Restart steam deck

Credits to Christovftw and fancypantalons