Gray card vs. ACR?

Can't you fix white balance on ACR or Lightroom? Do you really need to set custom white balance for tricky situations or do I suck at editing? Because whenever I take a picture in my room it's green and when I edit it looks better but still slightly green. And I started to wonder, maybe that's why there's sth named custom wb right? Should I use that?

Do a Custom White Balance when you can't get it right in post or when it's critical and you can't take chances.

Shoot RAW and you can always get it right in post as long as your monitor is calibrated and you have eyes.

To do a good WB in ACR you need to have a neutral grey or unclipped white object in the photo, either because you have placed it there or because by chance it's there. ACR's Auto WB works similarly to the camera's AWB, sometimes o.k., sometimes not - it depends on the distribution of colors in the image. Presets are also hit or miss. If you have a grey target in one photo you can use the dropper to determine WB and then batch apply it to a group of images shot in the same light.