I think that decision was wrong, but I don't think we can necessarily use that as a template for future SCOTUS decisions about the things Trump might do. During his first term (even after he'd appointed justices), there were still rulings that went against Trump's administration. Just as during Biden's time in office, there were rulings in favor of his administration. While I do not like the ideological bent of the current Supreme Court, it is not clear that they are in favor of the dismantling of government through illegal means.

(A nit: the word you're looking for is "rein", as in the thing you hold when riding a horse, not "reign", the ruling period of a monarch.)

The article you attached does not say that the ruling gives the president immunity from all crimes committed while in office.