Workshop addon and MultiAddonManager
How players get the menu: the Workshop addon, MultiAddonManager and what to do when players see an old menu.
The menu's layout and styles live in a small Steam Workshop addon (about 2 MB). MultiAddonManager tells each player's game to download it while they connect. Players don't subscribe to anything themselves.
Set the Workshop ID
Put the current menu's Workshop ID in SkinStudio.json:
"WorkshopAddonId": "<Workshop ID from your portal>",The plugin registers it with MultiAddonManager on every map start, so you don't need to edit MultiAddonManager's own config. With "ManageMultiAddonManager": true (the default) it also turns on MultiAddonManager's download cache, so players don't download again on every map change, and hides the "left the game" messages the download reconnect causes.
Add it to game/csgo/cfg/multiaddonmanager/multiaddonmanager.cfg. Note the name: mm_client_extra_addons (client only), not mm_extra_addons, which would also mount it on the server.
mm_client_extra_addons "<Workshop ID from your portal>"Check it
css_studio_status shows the Workshop ID the plugin uses and what MultiAddonManager has registered. css_studio_addon registers it again without a restart.
When the menu changes
CS2 doesn't update a Workshop addon a player already has. That's why every new version of the menu is published as a new Workshop item with a new ID. The changelog and the install guide always show the current ID; when it changes, update WorkshopAddonId and restart.
The menu shows its version at the bottom left (for example "UI 2.3.3"). If a player sees an older one, they have an old download; deleting steamapps/workshop/content/730/<old ID> on their PC fixes it.