I have the same issue. I have 4 devices (a Steam Deck, a Windows 11 laptop, a Bazzite desktop and a Bazzite HTPC) all running the stable build of Steam. I have non-steam games from other devices showing up on all of them, despite Remote Play not being enabled.

I'm also ending up with multiple copies of some non-steam games when they get synced. Today on my desktop PC there were 7 copies of several non-steam games which I added to my HTPC... so in addition to syncing when they shouldn't, they also seem to be duplicating themselves somehow.

Same here. I have GOG games added to Steam on one CachyOS machine, and I'm seeing them available to stream on two other CachyOS machines as well as a Win11 machine, despite Remote Play being disabled on all of them.

In case it's useful to know, I would like to add that when grouping my library by category, the games in question are also showing up as "Uncategorized" on the remote machines, despite definitely being in a category (they are in the correct category on the machine where they are installed).

EDIT: Additionally, there are some games showing up as available to stream that are NOT installed on the machine that it lists. (i.e., on MachineX, the library says "Stream from: MachineY," but the game is only installed on MachineZ.) I noticed this with a recently installed proper Steam game, not one of the GOG ones.

Same issue. Happening across three Windows 11 machines, two SteamOS machines, and a macOS machine. Entries that are hidden or deleted are restored after client restarts. Remote play disabled makes no difference. "Ready to Play should include streamable games" disabled makes no difference.

Having the same problem on my PC and Steam Deck. It has completely flooded my library with duplicate non-Steam games... please fix this.

Is there any way to fix this short term? I now have three or more duplicates of my non-Steam games in my library and it is quickly making it unnavigable.

I have a work around, you can close your steam (where the multiple copy are) and reopen it (full close, you need to shutdown steam).

If your steam deck is closed, the added apps won't be here. However, once you use your steam deck, it'll reappear. I kind feel like I need copy appear each time I use my steam deck.

Confirmed that the workaround @pal-cathar suggested does work; if the "source" machine is not currently running Steam, the non-Steam games don't show up on other systems anymore. I can even start Steam on the source again and the games won't show up on others until restarting Steam (on the "other" machines).

This obviously doesn't solve everyone's problems, but if you're like me and have the offending games installed on a machine that doesn't get used very much, it's a useful temporary solution.

Same issue across two Decks (Stable) and one SteamOS PC (Main). One workaround I found is to enable Remote Play on all affected devices, then turn it off again. Works until the next restart.

EDIT. Checked again with two clients I have access to at the moment.

A is SteamOS 3.9 build 20260519.1000, Steam Client version 1778803745.
B is Manjaro Linux, Steam Client version 1778281814.

I add something random, like Dolphin or Vim, to the library on machine A, it immediately appears on B.
I try the same on machine B, it does not pop up on A.

EDIT2. Updated B to Beta 1779155395, the issue appears to be gone.

Appears to be fixed for me after the latest Steam Deck update.

Appears to be fixed for me after the latest Steam Deck update.

Also seems fixed here.