According to your doctor, abilities, and not endurance level. Athletes can have low heart rates, due to enhanced Parasympathetic Tone and good Ejection Fraction.

This individual is an Electrophysiologist:

The Mysterious Athletic Heart
https://www.drjohnm.org/the-mysterious-athletic-heart/
He details how Endurance Level Exercising can cause Afib and dangerous heart rhythms. But overall, in those approved, non-endurance exercise can be good.

The following link, I'll spoil it, he says the best tool to treat afib is education. Since he's a doctor that does ablation, and since, while, essentially endurance exercising on a Bicycle, he went into afib, I figure he knows both the doctor and patient sides. He advocates for restraint in seeking treatment, I'm sure commensurate with the patient's situation. This was a relief to me in reading it. I hope that MayoClinic finds this suitable, I'm not sure of their policy. If questionable, I hope they review the site, it has much to add without advertisement. The doctor was cardioverted, but he said that if still in afib, he couldn't do the ablation that is his profession.

The best tool for treating atrial fibrillation
https://www.drjohnm.org/2011/03/the-best-tool-for-treating-atrial-fibrillation/