Do you add a separate dose of losartan for patients with heart disease and proteinuric kidney disease who are on maximal doses of sacubitril/valsartan but continue to experience proteinuria?  

There is data in studies of proteinuric kidney disease to suggest that combining an ACEi and an ARB confers a little additional benefit in proteinuria management but confers a significant risk of hyperkalemia. I would presume the same risk/benefit ratio when using 2ARBs and I would not opt for that ...

I do not add an additional ARB if they are already on one. In this situation, I would add an SGLT2 inhibitor for both the proteinuria and heart disease. If the patient is already on an SGLT2 inhibitor and has diabetes, then I would consider adding finerenone for the proteinuria.

I do not. I don't believe 2 separate ARBs are better than one. For me the most important factor with proteinuric CKD is to control the blood pressure to as low a range that will minimize the proteinuria. This often requires good doses of diuretics. 

To add to this, my understanding is that one of the reasons that the valsartan dose is not maxed out by the manufactuers is because sacubutril affects the same pathway of metabolism of substance P and bradykinin, which increases the risk of adverse reactions. By adding more ARB, we potentially incre...

I would add SGLT2 I to reduce proteinuris and or consider the addition of spironolactone if BP is uncontrolled.

I would add finerenone, as it reduces proteinuria and fibrosis of the kidney through its actions as an MRA. If the patient's blood pressure is not well controlled, I would add a nondihydropyridine calcium channel blocker to further reduce the patient's proteinuria and blood pressure.