Optimum Realism works in singleplayer but not on a server or realm — why

Optimum Realism is a client-side resource pack: it lives in your game, not on the server. On a normal multiplayer server it keeps applying exactly like it does in singleplayer. So if it works solo but vanishes the moment you join a world, the server is overriding it.

What's happening: a server (via server-resource-pack in its config) or a realm can send its own pack to everyone who joins. When it does, that server pack sits on top of your selection and replaces the textures — including swapping Optimum Realism's blocks for the server's own, or for the pink/purple "missing texture" look if the server pack is incomplete.

Two flavours of this:

• Optional server pack — you get a prompt to download it. Decline, and you join with your own Optimum Realism textures intact.
• Required / forced pack — the server or realm makes its pack mandatory to join. Here the override isn't something you can switch off from your side; it's controlled by the server or realm owner.

What you can do:

• If you see a "this server has a resource pack" prompt, you can decline it (when it's optional) to keep your own pack.
• On a forced server/realm, ask the owner to make the pack optional, or to add Optimum Realism for everyone. Realm packs in particular are owner-controlled and pushed to all players.
• If only some blocks turn pink/purple on a server, that's the server's own incomplete pack, not yours — same fix applies. See pink / purple blocks.

Bedrock note: Bedrock applies packs per-world, and a world or realm pack outranks your global selection. If you're on Bedrock, the world-pack priority fix is here: world / realm overriding the pack.