Ubuntu 22.04 LTS was released on the 22nd April 2022 and whilst Ubuntu has been installable on Raspberry Pi 4 models with at least 4gb RAM, only now is Ubuntu officially supported on Pi 4 models with 2GB of RAM. This is due to zswap being enabled by default in Ubuntu 22.04. Zswap is essentially a compression tool which canonical explains as:
When a process is about to be moved to the swap file, zswap compresses it and checks whether the new, smaller size still needs to be moved or if it can stay in your RAM. It is much quicker to decompress a ‘zswapped’ page than it is to access the swap file so this is a great way of getting more bang for your buck from systems with smaller amounts of RAM.Oliver Smith on 11 January 2022 (Ubuntu.com)
This being said, a 2GB RAM model Raspberry Pi 4 may not provide as good of a desktop experience as Ubuntu running on the 4 or 8GB models. Take a look at the Ubuntu guide for installing Ubuntu 22.04 on the Raspberry Pi 4, either via micro SD card or external hard drive or SSD, here.