Audio interfaces usually have what you need but their mic inputs are either 1/4” or XLR. You probably need a converter for it. Products from M Audio and Rode ranges from anywhere below 300 to a few k.

The FiiO has Optical in and USB in

TV > FiiO (via optical)
PC > FiiO (via USB)

FiiO > Active Speakers (via RCA)

Use the front panel to switch inputs between USB and Optical. Use the volume knob to adjust volume.
That's a good starter unit with a lot of input options. Can use the headphone out too if you have one. (I think it mutes the RCA out if you plug in headphones but I'm not sure)

If you replaced the RCA cable and the crackling problem persisted, it could be faulty speakers.
The DAC/amp would be good to improve sound quality but I'm concerned it might not solve your crackling problem.

Try to connect your tv to your speakers via Optical and see if the crackling persists.

Oh wow that's very weird. But then if you connect your PS5 straight to the speakers are there any noise?

If we're talking about airborne interference like electromagnetic waves or radio frequencies right, it won't affect line level signals that much. For phono connections like turntables, those are more susceptible to noises if no proper shielding and grounding.

But if that happens intermittently (like you said maximise video window will cause crackle) then it could mean your computer headphone output is noisy.

If your computer has some polluted power, like sometimes you can feel current on the case, or there's current leakage in the grounding, a USB DAC might help.
Is it a gaming pc kind with power hungry components?