Had the same issue and running isql under LD_DEBUG=libs showed exact place where the lib failed to load. Command like

"LD_DEBUG=libs isql host user pwd -v"

In my case the error was:

  2574:     find library=libffi.so.7 [0]; searching
  2574:      search path=/opt/conda/bin/../lib              (RPATH from file isql)
  2574:       trying file=/opt/conda/bin/../lib/libffi.so.7
  2574:     
  2574:     /usr/lib/x86_64-linux-gnu/libp11-kit.so.0: error: symbol lookup error: undefined symbol: ffi_type_pointer, version LIBFFI_BASE_7.0 (fatal)
  [01000][unixODBC][Driver Manager]Can't open lib '/usr/lib/x86_64-linux-gnu/odbc/libtdsodbc.so' : file not found

Conda installation affected link to libffi.so.7 (actually goes to 8.x version)

So I had to remove 2 so.7 files (links actually) in conda directory like in https://stackoverflow.com/a/75045665 ansert, Zhanwen Chen comment. And it works smoothly after that.