The RLMM (Robust Linear Mixed Models) is a R package that fits longitudinal data using robust loss functions such as Huber and Tukey.
I.M. Danilevicz, P. Bondon, V. A. Reisen, F. Sarquis. A longitudinal study of the influence of air pollutants on children: A robust multivariate approach. Journal of Applied Statistics, 2023, https://doi.org/10.1080/02664763.2023.2272228.
RLMM is only available on Github, there is a package on Bioconductor, but it is another package from other authors.