Therefore, the federal government can't prohibit individual citizens from owning firearms.

We end up with individual rights to keep and bear that are unconnected to the militia because the prefatory clause has no effect on the operative clause of to keep and to bear. The Constitution outlined the Militia:

Section 8.
Clause 15. The Congress shall have Power * * * To provide for calling forth the Militia to execute the Laws of the Union, suppress Insurrections and repel Invasions.

Clause 16. The Congress shall have Power * * * To provide for organizing, arming, and disciplining, the Militia, and for governing such Part of them as may be employed in the Service of the United States, reserving to the States respectively, the Appointment of the Officers, and the Authority of training the Militia according to the discipline prescribed by Congress.

So this is the Constitutional militia. And under Ch 12 of the Federal Code it is all able bodied men between 17 and 45. Modernly, the organized militia in the code is the National Guard, and the unorganized militia is the pool of able bodied men (17-45) that both the Federal Government and the State can draft from and enlist. There are a few bodies that might be considered militia - DeSantis' State Guard if he turns it military (looks like it), but there are no private or self appointed militia. The States had dealt with Shays rebellion and kept that power to themselves and the Fed.

So the individual right is based mostly on self defense. The easier way to deal with the second amendment is to alter it from a right that seems to be sacrosanct to one that can be limited. Trying to repeal or amend it is too hard, but we can interpret it so it can be limited.