Reproduction steps:
1. Open the attached project “LibdlTest.zip”
2. Open “Assets/Scenes/SampleScene.unity” scene
3. Click File > Build Settings…
4. Click “Add Open Scenes”
5. Select the “Development Build” checkbox
6. Click “Build And Run”

Expected results: Player is run without any errors in the development console, and there are no “Fallback handler could not load library” errors in Player.log
Actual results: The development console shows a “DllNotFoundException” error when the Player is run, additionally you can also see “Fallback handler could not load library” in the Player.log (see the logs below)

Reproducible with: 2021.3.34f1, 2022.3.17f1, 2023.2.0a22 (has “Fallback handler could not load library” error), 2023.2.0a23, 2023.2.7f1, 2023.3.0b4 (doesn’t have the “Fallback handler could not load library” error)

Reproduced on: Ubuntu 22.04.3

Logs:
Fallback handler could not load library <path/to/project/build>/test_Data/MonoBleedingEdge/x86_64/libdl.so
Fallback handler could not load library <path/to/project/build>/test_Data/MonoBleedingEdge/x86_64/libdl
DllNotFoundException: libdl assembly:<unknown assembly> type:<unknown type> member:(null)
at (wrapper managed-to-native) Silk.NET.Core.Loader.Libdl.dlopen(string,int)
at Silk.NET.Core.Loader.LibraryLoader+UnixLibraryLoader.CoreLoadNativeLibrary (System.String name) [0x00000] in <60b219252eb448c2b8060c9769dd10a2>:0
at Silk.NET.Core.Loader.LibraryLoader.LoadWithResolver (System.String name, Silk.NET.Core.Loader.PathResolver pathResolver) [0x0003b] in <60b219252eb448c2b8060c9769dd10a2>:0
at Silk.NET.Core.Loader.LibraryLoader.TryLoadNativeLibrary (System.String[] names, Silk.NET.Core.Loader.PathResolver pathResolver, System.IntPtr& result) [0x00017] in <60b219252eb448c2b8060c9769dd10a2>:0
at Silk.NET.Core.Loader.LibraryLoader.TryLoadNativeLibrary (System.String name, Silk.NET.Core.Loader.PathResolver pathResolver, System.IntPtr& result) [0x00000] in <60b219252eb448c2b8060c9769dd10a2>:0
at Silk.NET.Core.Loader.UnmanagedLibrary.TryCreate (System.String name, Silk.NET.Core.Loader.LibraryLoader loader, Silk.NET.Core.Loader.PathResolver pathResolver, Silk.NET.Core.Loader.UnmanagedLibrary& library) [0x00000] in <60b219252eb448c2b8060c9769dd10a2>:0
at Silk.NET.Core.Contexts.DefaultNativeContext.TryCreate (System.String name, Silk.NET.Core.Contexts.DefaultNativeContext& context) [0x0000b] in <60b219252eb448c2b8060c9769dd10a2>:0
at Silk.NET.Assimp.Assimp.CreateDefaultContext (System.String[] n) [0x00006] in <5427bd99fee74d529b57dc204b026d9d>:0
at Silk.NET.Assimp.Assimp.GetApi () [0x0000a] in <5427bd99fee74d529b57dc204b026d9d>:0
at MainScript.Start () [0x00001] in </path/to/project>/Assets/MainScript.cs:10

Workaround for “DllNotFoundException”: copy local libdl.so.2 file found with ‘whereis libdl.so2’ command to the directory where the “Fallback handler could not load library“ error is happening. For example:
$ whereis libdl.so.2
libdl.so.2: /usr/lib/x86_64-linux-gnu/libdl.so.2 /usr/lib32/libdl.so.2
$ cp /usr/lib/x86_64-linux-gnu/libdl.so.2 <project build directory>/test_Data/MonoBleedingEdge/x86_64/libdl && cp /usr/lib/x86_64-linux-gnu/libdl.so.2 <project build directory>/test_Data/MonoBleedingEdge/x86_64/libdl.so && cp /usr/lib/x86_64-linux-gnu/libdl.so.2 <project build directory>/test_Data/MonoBleedingEdge/x86_64/libdl.so.2

Note: from 2023.2.0a23 versions, the “Fallback handler could not load library” disappears, and only “DllNotFoundException: libdl” remains which can be fixed with the previous workaround.