Checking the Assumptions of a Mixed Effects Model in R

Hi all was hoping of a little bit of advice here.
As far as I am aware, 4 of the assumptions of a mixed effects mode are:
-Normally distributed residuals
-Heteroskedasticity of residuals
-Normally distributed residuals of the random effects potion of the model (i.e. Blups)
-Heteroskedasicity of the random effects potion of the model (i.e. Blups)

Is this correct? If so, then how would you test for it in R?
I am struggling the most with the last one, as I can get qqnorm plots for looking at normality. I have been using the package 'nlme' -


I think I also figured how to plot the fitted residuals against the he fitted residuals against the residuals to check heteroskedasicit



Is this correct? What would this look like if the assumption of homoskedasicity was met?
And how do I get R to run this in the random effect residuals instead?

Many thanks!

Hi, and welcome!

Preliminarily, see FAQ: What's a reproducible example (`reprex`) and how do I do one? for how to attract more answers by reducing the setup time to recreate the problem and better understand the question.

Take a look at this vignette from the DHARMa package for a discussion of the issues.

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