In the Chauvin trial, why they have not talked about Chauvin and Floyd working together as security guards at the same club? ?

The prosecution would need evidence to put before the court.  There's no point mentioning it if it provides no evidence.  You are right it could provide a motive for murder, if circumstances generated one.  Maybe they did not know each other.

Somebody has been stalking this question to get rid of answers they don't like; Myra Spyra and her buddies.

Because the media is cherry picking the trail. The liberal media won't cover anything that doesn't make Chauvin appear guilty, like the body cam footage that exonerated the officers.

That's an interesting idea. Maybe they'll ask Chauvin himself when he testifies.

A previous feud between them is not important except as it might go to motive.  First they have to decide whether Chauvin did, in fact, cause Floyd's death in whole or in part.  And if so, whether it was deliberate, or a case of recklessness [depraved heart] or an accident.  

Only if it is found that Chauvin deliberately or recklessly caused Floyd's death would any relationship between them be relevant.  And even then, it would not be necessary to the case.  He could be convicted even if his motivation is not known.