Hello,
As per me you have to create a skin using a skin editor or download one from sites like Minecraft Skins. Open the Minecraft Launcher, go to the "Skins" tab, and click "New skin" to upload your custom file. After saving the skin, it will be applied in the game.
Hello,
I think you can try running Aristois without any other mods to see if the Right Shift issue persists. If it works fine, reintroduce your other mods one by one to identify the conflict. Make sure all mods are compatible with Minecraft 1.20.4 and are updated to their latest versions.
The addons marketplace is not for Forge anyways. You would have to download the Forge version of Baritone (forge-api) from their GitHub and add it to your mods folder.
If you join our Guilded server you can find instructions here: https://www.guilded.gg/aristois/groups/PdYbEW7z/channels/79aac8a3-d86f-4c5f-92e5-02ed40555c57/forums/63622808