Ubuntu:

sudo apt install xrdp 
sudo adduser xrdp ssl-cert 
sudo systemctl restart xrdp

Fedora:

Install pacakge

sudo dnf install xrdp xorgxrdp

Configure firewall

sudo firewall-cmd --permanent --add-port=3389/tcp
sudo firewall-cmd --reload

Configure SELinux

sudo chcon --type=bin_t /usr/sbin/xrdp
sudo chcon --type=bin_t /usr/sbin/xrdp-sesman

/etc/X11/Xwrapper.config

# ...

# Allow anybody to start X:
allowed_users=anybody

/etc/xrdp/xrdp.ini

Uncomment the lines for [Xorg]

;
; Session types
;

; Some session types such as Xorg, X11rdp and Xvnc start a display server.
; Startup command-line parameters for the display server are configured
; in sesman.ini. See and configure also sesman.ini.
[Xorg]
name=Xorg
lib=libxup.so
username=ask
password=ask
ip=127.0.0.1
port=-1
code=20

xsession

cp /etc/X11/xinit/xinitrc ~/.xsession

replace the last if -fi section with desktop startup command

Example full working config:

# File: ~/.xsession

#!/usr/bin/sh
# Copyright (C) xxxx

# Mandatorily source xinitrc-common, which is common code shared between the
# Xsession and xinitrc scripts which has been factored out to avoid duplication
. /etc/X11/xinit/xinitrc-common

exec dbus-run-session -- startlxqt

Restart services

sudo systemctl restart xrdp
sudo systemctl restart xrdp-sesman

Archlinux

Install pacakge

yay -S xrdp xorgxrdp-git

/etc/X11/Xwrapper.config

# ...

# Allow anybody to start X:
allowed_users=anybody

/etc/xrdp/sesman.ini

# ...
[Xorg]
param=/usr/lib/Xorg
# Leave the rest of the lines untouched
#...

xinit

cp /etc/X11/xinit/xinitrc ~/.xinitrc

~/.xinitrc

# ...

# !!! Remove several lines from "twm" to "xterm",
# !!! since we don't need them and they throw error if not removed

# Start Desktop Environment
exec dbus-run-session -- startplasma-x11

Enable + Restart services

systemctl enable xrdp
systemctl enable xrdp-sesman
systemctl restart xrdp
systemctl restart xrdp-sesman

More info: https://wiki.archlinux.org/index.php/Xrdp