My reading of the research on GLP's in general , as there is a lot less research specifically on retatrutide, is that there really is no significant overall effect on mood, incidence of depressive illness or suicidal thoughts or actions. Except for an improvement in mood with significant weight loss, that happens regardless of the cause of that weight loss.
Individual variation of response to GLP medications is fairly large, and there are a lot of anecdotal reports on this forum for example of it causing fatigue or anhedonia.
Mood is really very responsive to placebo effects, many antidepressant trials have positive response rates of 70% for the active drug and 50% for placebo for example.
I would guess that this effect is probably stronger than any actual biological effect on mood, so your expectations going into using the medications is important.
Given that the original poster was concerned about the effects on mood before starting reta, the odds of it causing issues is increased, due to an expectation related nocebo effect.
I would say that the evidence so far suggests there is no substantial effect on mood except for improving it once weight loss occurs. And don't worry about it unless it happens and then you can easily stop it or try a different GLP.