The answer to this question depends on how the question itself is interpreted. Here are 3 ways it could be answered...
(1) One answer is: there are not any. Because it’s a bit like asking the question: ‘what are the main alternatives to gravity? Or evolution?’ DSRP isn’t a framework, it’s a factual reality. Identity-other Distinctions, part-whole Systems, action-reaction Relationships, and point-view Perspectives exist in mind and nature. They occur naturally whether we like it or not. You think in DSRP whether you choose to or not. Or whether or not you’re aware of it.
(2) But of course we could ask the question, ‘what are the main alternatives to evolution?’ And answer: well, one alternative view is creationism where God created all the creatures and Adam and Eve spawned humanity from the garden of Eden. Technically speaking, that is an ‘alternative.’ But it’s not a legitimate scientific alternative.
(3) You could treat DSRP as merely a framework, rather than the universal Theory that it is and answer the question a third way (which is likely what is meant most often). In this way, the question, ‘What are the main alternatives to the DSRP?’ gets a a different answer which is:
If DSRP is just a framework there are thousands of systems thinking frameworks. The most popular ones are system dynamics (SD), soft systems methodology (SSM), critical systems thinking (CST), etc. There are many many more. But this answer misses the critically important point DSRP is making: that DSRP structures are universal to all of these frameworks. There is no evidence that these frameworks exist in mind and nature (indeed, there is more often than not, very little empirical evidence at all for these frameworks—mostly just effectiveness studies). There is a growing abundance of empirical evidence that DSRP structures do exist in both mind and nature. Occam’s, for example, bodes well for DSRP Theory and is not good for these other frameworks.
 Cabrera, D., Cabrera, L., and Cabrera, E. (2021) A Literature Review of the Universal and Atomic Elements of Complex Cognition. In, Routledge Handbook of Systems Thinking, (Eds) Cabrera, D., Cabrera, L. and Midgley, G. Routledge. London, UK.