A Genshin Impact YouTuber Mockermay published a video "guide" showing you the way to get Paimon to follow your side like a true companion such as the Seelies, Endora, Shiki Koshou, and more.
However, you must not start the new Fungi Mechanius event in Genshin Impact version 3.5 in order for this bug to work. To get this Paimon companion, you will need to be on the bridge above Paimon and the two Fungi in Port Ormos.
Enter the co-op mode and jump down on top of Paimon while opening up the menu at the same time. Your first character will die due to the height and as soon as your second character swaps in, a new Paimon will float next to you.
(source: Mockermay)
You may also quit the co-op mode after obtaining the Paimon companion and keep it along as soon as you don't open up the menu again. Also, check out the video for more detailed info about this bug.
Source: Mockermay, PCGamesN
