Squeezing interval change from ordinal panel data in R

Question

Due to model identification I would need to freely estimate both means and variances and also thresholds of my ordinal variable with (3 categories).

I have read that "when having more than 2 categories, threshold information can be used to estimate the mean and variance of the liability rather than fixing them" in this paper https://pubmed.ncbi.nlm.nih.gov/15355151/

In this paper Mx scripts are provided but I am not able to translate it to R

I just wondered if there is any function or package in r to do that or how I could do it.

Any guidance would be really appreciated. Thank you so much in advance.

With all good wishes,