Google's John Mueller was asked if adding cookie acceptance banners are going to cause an SEO problem for Google search. John said "Cookie banners are fine." He added that you want to avoid "replacing your page's content with an interstitial." If you do use an interstitial that replaces your content on your page, Google won't see the content.
Here are those tweets:
Cookie banners are fine. The thing to avoid is replacing your page's content with an interstitial - then we just won't be able to index the content at all.
— 🍌 John 🍌 (@JohnMu) January 16, 2020
This is the same for GDPR notifications.
Lots and lots of sites are showing small banners for cookie consents since January 1st. So Google is handling them.
Forum discussion at Twitter.