Currently for players who want to make GUI in Skript, TuSKe addon is a good option, but it is very outdated and buggy.
Making GUI in vanilla Skript is not an option for many simply because it is too complicated or requires too much work.
There is a fork of TuSKe's gui manager which is maintained: skript-gui
https://github.com/APickledWalrus/skript-gui/releases/latest
I request that this plugin be added.