R version 3.5.3 is rather old, and you are likely to experience compatibility issues. I highly suggest updating.
The CRAN record for {markovchain} package - https://cran.r-project.org/package=markovchain - states that the package depends on R version 3.6 or higher (it is translated from the package DESCRIPTION file).
If you absolutely positively require R 3.5.3 you might be able to install an older version of the package, but an R update should be your first choice.