Calculation of reliability of scale scores in an IRT- model While trying to compute the reliability of scale scores obtained from IRT models (bifactor models and unidimensional models) I was wondering why there are so many published papers who report omega categorical/ omega hierarchical or even cronbachs alpha, even though those are reliability estimates conducted unter a CTT approach?
Which reliability coefficient is recommended for scale scores and how do I compute it in RStudio?

They're reported because people expect them and reviewers ask for them. It's a  single summary indicator of how well the scale hangs together - it's not ideal, but it's not (IMHO) useless. If the reliability estimate is 0.5 or 0.9, that tells you something.
For the second part of your question, does this answer help: Reliability in IRT Style
