尝试安装时libsdl2-2.0:i386，我遇到了这个问题
Reading package lists... Done
Building dependency tree
Reading state information... Done
Note, selecting 'libsdl2-2.0-0:i386' for regex 'libsdl2-2.0'
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:
The following packages have unmet dependencies:
libsdl2-2.0-0:i386 : Depends: libasound2:i386 (>= 1.0.27)
Depends: libsndio6.1:i386 (>= 1.1.0) but it is not going to be installed
E: Unable to correct problems, you have held broken packages.
sudo apt install libsndio6.1:i386调查后我发现
The following packages have unmet dependencies:
libsndio6.1:i386 : Depends: libasound2:i386 (>= 1.0.17)
E: Unable to correct problems, you have held broken packages.
sudo apt install libasound2:i386导致
The following packages have unmet dependencies:
libasound2:i386 : Depends: libasound2-data:i386 (>= 1.1.3-5)
E: Unable to correct problems, you have held broken packages.
但我遇到了麻烦，因为尝试安装时libasound2-data:i386我得到了
Note, selecting 'libasound2-data' instead of 'libasound2-data:i386'
libasound2-data is already the newest version (1.1.3-5ubuntu0.1).
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
这是在全新安装的 Ubuntu MATE 18.04 LTS 上进行的，Software Boutique 中的“损坏的软件包”修复没有帮助。
编辑：我通过删除 libasound2 和 libasound2-data（64 位版本）解决了我的问题——没有删除依赖包（这会删除整个系统），然后重新安装它们（再次安装 64 位版本）。现在 32 位版本安装正常，SDL2 32 位版本安装正常。不要问我为什么。
事实证明版本错误，但它拒绝在 Synaptic 中升级/降级，所以这样做是我能想到的唯一方法。
但是我在尝试安装另一个 32 位库时遇到了同样的问题！因此，如果有人有永久解决方案，我会继续提出这个问题...