Hello!
Just a simple tutorial as I saw someone in the discord asking about it - you can play custom maps other than Eric's test map in the latest version of the game with new guns and skins, there's just a simple trick to it.
So, to play the demo you hit this link: https://www.plazmaburst2.com/?s=2&exper ... t-testtest
You'll be taken into the demo version of the game. However, before you select difficulty level, you should click cancel on the bottom left of the screen.
You are now free to use the game in the same way as any normal non-demo version to test 1.28 maps. This tutorial is only valid until the update comes out, but the same trick may work on future game version demos. Also, I haven't tried multiplayer using this method yet, so whether it works or not is unknown to me.