Brukinsa is also known as Zanubrutinib. There are few members in the forum who have experience with this medication and most are in this discussion about Waldenström's Macroglobulinemia.

You’ll have to scroll back a little but here are the comments I’ve found with @pldgsph @newwaldenguy and @sidm. Below, I’ve provided the direct links that reference Brukinsa/Zanubrutinib
https://connect.mayoclinic.org/comment/746825/
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https://connect.mayoclinic.org/comment/746430/
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https://connect.mayoclinic.org/discussion/waldenstrms-macroglobulinemia/?pg=4#comment-830226
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https://connect.mayoclinic.org/comment/830461/
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And this from @sunfishgirl who was being switched to the medication a month ago.
~Want to connect with others with Splenic B cell Marginal Zone Lymphoma
https://connect.mayoclinic.org/comment/799826/
From the comments I read, it appears that this is a well tolerated drug with some positive results. I know you and your husband have reservations about starting this new medication because of Afib and other complications. Has this been run past his cardiologist?

I am sorry you are experiencing multiple issues to balance with a new treatment. I have WM and have not had Brukinsa.