Visit https://www.arduino.cc/ to download Linux 64 bits version.
Extract the downloaded file and more to where you want. Switch to the folder and run:
$ sudo ./install.sh
You will be reported with error of:
An error occurred while uploading the sketch
avrdude: ser_open(): can't open device "/dev/ttyACM0": Permission denied
You can add you (the user) to the group own permission of the upload port:
$sudo usermod -a -G dialout <username>
$sudo chmod a+rw /dev/ttyACM0
change username and ttyACM0 according to your setup.
logout and login.
Basically, the steps to install Arduino IDE on Ubuntu 20.04 are same as install on previous version of Ubuntu. But if you target to develop for ESP32/ESP8266, very likely you will be with error of:
exec: "python": executable file not found in $PATH
ModuleNotFoundError: No module named 'serial'
Check next post - Install ESP32/ESP8266 to Arduino IDE on Ubuntu 20.04, with setup Pythton & serial