The solution seems to be related to memory management. BigInteger works in the background with ArrayPool.Shared.Rent. If BigInteger is too busy with new memory being generated, the result of the mathematical operation can be written over the number on the left or right. However, to perform such an operation, it may be necessary to start coding with masm rather than BigInteger. Sample masm project links:

https://github.com/bestprogramming/BigIntAddition https://github.com/bestprogramming/BigIntMultiplication