MSVCR100.dll is the C runtime library from Microsoft's Visual C++ 2010 package. Older games and tools built with Visual Studio 2010 need it to start, and the usual "was not found" message means the 2010 redistributable was never installed on this PC, or an uninstall or cleaner removed part of it.
Look inside the failing program's folder for its own copy of MSVCR100.dll. Some programs ship a private copy, and if that copy is older or damaged it overrides the healthy system one. Rename it (add .bak) so the program falls back to the system DLL, then relaunch. If only one program fails while others work, that program is damaged, and a clean reinstall is the remaining move.
Is the 2010 redistributable still available from Microsoft? Yes, Microsoft still lists the Visual C++ 2010 Redistributable Package on its download site, in x86 and x64 versions. Get it from Microsoft, not from a DLL site.
Will the newer 2015-2022 redistributable fix it? No. Each Visual C++ generation is separate, and the 2015-2022 package does not contain the 2010 files. A program that asks for MSVCR100.dll needs the 2010 package specifically, installed alongside any newer ones.