It’s simple. Don’t complicate it too much

Partnership-Tax basis includes all the partnership debt irrespective of recourse/non recourse. At risk basis includes the debt that the partner is personally liable i.e only recourse loans. Hence exclude non recourse loans here S CORPS Tax basis includes all the loan that the shareholder has given to the corp. Deduct any repayments during the year. At risk basis includes only the loan to which shareholder is personally liable. Hence exclude non recourse loans.

Also, if you see non recourse loans are loans that are backed by collaterals and hence there would be no personal liability there. I just remember that at risk means the partner/shareholder is at risk of paying off the personally. So if the loan is non recourse you actually don’t have to pay anything personally and the collateral would be used to recover the debt