How do I connect a mixer (cinch output) to a laptop (jack microphone input)?

I have a mixer, which I connect via a 2x RCA cable output and an adapter to the 3.5mm jack microphone input (I have specially procured a USB sound card).

To record simple voice recordings at the event.

Problem:

The signal arrives, but there's a constant whirring. I've already tried everything, but it's not on the new notebook.
When I connect the cable to a portable recording device to the 3.5mm jack input, it works properly without humming and sound is transmitted clearly

Where is the mistake?
Both devices are connected via the same line. The same signal: Recordings on the portable recording device work great and neat

A microphone input is far too sensitive and is simply overdriven. You need a "line" input for this

Ok, strangely, the whole works smoothly with a portable Olympus recording device. This also has a microphone input as a jack.
Would it work with such an external device? https://www.musicstore.de/de_DE/EUR/Behringer-UCA202-U-Control/art-PCM0005351-000?campaign=GShopping/DE&ProgramUUID=rrLAqJarLjMAAAFl.gZyjI8h