The system has specific, well-defined checks and balances. For example, Congress can limit the executive’s control over spending by enacting specific appropriations bills with concrete line items. But it hasn’t done so for decades. It has done things like appropriate single $1.7 billion line items for USAID, leaving it to the executive’s discretion how to spend it with only the vaguest guidelines. Congress having done that, it’s not for say the courts to “check” that by insisting that the executive can’t exercise all the discretion Congress provided it.

And your point about immunity is misinformed. The Supreme Court held that the President has immunity for official acts. This is a no-brainer. You can’t sue Congressmen for their official acts either, or judges.

If the President didn’t have immunity, Georgia prosecutors would be able to indict and convict Joe Biden in some red county in connection with the murder of Laken Riley, on the theory that Biden recklessly or negligently opened the border leading to her death.