I did a quick search on LW but didn't find any important article about information diet. Did I miss something?

I found a post that might be talking about the capital-I capital-D Information Diet you might be talking about.

There've been some other threads and a post about cutting down on news or eliminating news from one's life, too.

Should we eliminate all news sources like some advocate?

It's actually very plausible to me that a little news is the optimal amount for most people to deliberately consume, but I do mean a little — maybe 5 minutes a day as an order-of-magnitude guess — and one is probably not going to miss out on that much by cutting down to literally zero (though in a given time & place it might be a bad idea).

I'm aiming for the soft spot of eliminating all the unnecessary news while still getting those pieces that are relevant for me.

The first idea which pops into my mind is specialization: pick news/commentary sources where a specialist talks about a narrow topic they know well. In your tax code example, you might be able to find some interesting tax bloggers(!) who'd be likely to mention important changes to the tax code in your jurisdiction.