SRAM Apex 1 doesn't upshift I have a Boardman CXR 8.9, everything stock except for new mech hanger.
It has a 11-42 cassette with a 11 speed 1x drivetrain. It's Sram Apex throughout, no mixing and matching like in other questions.

The issue is - while downshifting (going from smaller to larger cog) works well, the opposite needs a "nudge" most of the time. The "nudge" could be stopping to pedal for several seconds or pulling the shifter cable and then letting it go.

Already tried to fix my shifting, changed the mech hanger (original was slightly bent) but neither helped. Rear derailleur still seems sticky.
It seems that others had the same issue, but the only suggestion (use a spacer) doesn't seem to apply to me, as it's already there (see picture)

Did I miss something?
That sounds like a sticky shift cable.

Undo the cable from the derailleur, check the derailleur itself is not sticking. You can do this by getting the rear wheel off the ground, pedaling manually and pushing the derailleur body inwards to change down to lower gears, then letting it come back to higher gears. Be careful to avoid catching your fingers in the chain. 

You could also do a quick check of the hanger alignment: from behind the derailleur sight down the chain. The cage should be parallel with the chainrings. This is difficult to do without the bike in a workstand, but you can get the same view by taking a picture with a phone. 

Pull the shift cable out and wipe it down, you can also introduce a small drop of lube into the housing. 

If that does not fix the issue consider repacking the housing and cable.