We know that Google says you can spam and stuff the meta keywords tag all you want, it won't cause a penalty because Google simply ignore the meta keywords tag. Thus, it is pretty obvious that using the meta keywords tag with real keywords relevant to the page is also not going to cause any sort of penalty.
But someone wanted to be sure that having a meta keywords tag on your page would not cause a Google penalty.
Gary Illyes from Google said don't worry, it won't cause a penalty. He said on Twitter no, it won't cause a penalty and added "but also not used for anything."
No, but also not used for anything
— Gary "鯨理" Illyes (@methode) June 21, 2018
So feel free to go crazy with the meta keywords tag, that is, if you don't care about other search engines that may use them or not - such as Bing.
Forum discussion at Twitter.
