I wasn’t able to reproduce this problem using a mostly empty project that just includes the “libCSteamworks.so” file, setup the same way shown - placed in “Plugins/x86” and marked for x86 only. Building for both linux x86 and linux universal showed libCSteamworks.so in the Data/Plugins/x86 folder.
What version of Unity are you building with in Unity Cloud Build? And locally? And just to rule it out - have you tried running a clean build in UCB?
Thanks for trying sir! I have another project with the same files that included them with a new Linux target I just made. I’m going to look into it a little more and I’ll get back to you if I can figure out what the difference is.