[kccqzy]

Green Hills Software has the Integrity operating system rated to EAL6+, which stands for "Semiformally Verified Design and Tested" so almost there but not quite.

But honestly it's not something you would want to use in daily life.

[heyjudy]

Not to the rigor seL4 has, with multiple-levels of verification.

[kccqzy]

Yes I agree, but still with significantly more rigor than your typical operating system (Linux, Windows, macOS).