Does anyone have experience with heart arrhythmia (AFib or flutter) and chronic nausea? No doctor can find the cause.

https://www.everydayhealth.com/copd/managing-copd-panic-attacks.aspx

Read this.

How often are they experiencing AFib/Flutter? Are there other heart problems as well? I know that my mother's primary symptoms of angina were always nausea and vomiting.

The odd thing is that they now know there is a connection between GERD (gastric reflux of "heartburn") and atrial fib. You can google about this. Is there any heartburn at issue here? It often causes nausea, as well.
I have never, as a nurse, or as a more than a few decades dealing with At fib both myself and my Partner, experienced nausea due to the atrial fib. So I doubt there is a connection. If you want to do a little research just "google" (or other search engine) gastric reflux and atrial fib. If anyone is seeing or exploring a connection it will be there.
I very much agree with MollyMoose that there could be an anxiety connection. Anxiety often causes nausea. Is this a new diagnosis of Atrial Fib that is worrying the involved person. The other thing to consider is medications. Are there new ones. Many meds cause nausea. It often is a temporary and mild reaction, but can be more if it continues.
This is definitely worth running past the doctors office as a question if the nausea is new. People with atrial fib become overly vigilant about "feelings" in chest and abdomen for a while at times.

Is it possible this brought on by anxiety? I’m on day three of my mother-in-law being in ICU, this morning being told her biggest problem is anxiety. This the second full scale work-up she’s had (including a heart cath, no blockages) in two years, only to be told it’s anxiety, although she does have COPD.