Twitter was positioning itself as a major gatekeeper of information, and so I do think the EU should be looking into this carefully in hopes of preventing it from happening again.
You might be more used to the more informal social media use of the word meaning busybodies that involve themselves unasked to police people's behaviors to their own arbitrary standards; this is not it.
> (by extension, slang, Internet) To limit another party's participation in a collective identity or activity, usually due to undue pettiness, resentment, or overprotectiveness.
But in the (today) rarer, less metaphorical sense... It's not that either? What is Twitter guarding access to? It's not, we're talking about Twitter itself.
From a straight up grammatical perspective, I'm not sure what you're saying makes sense, or really what you're trying to say. What you're saying "gatekeeper" means tracks just fine. But I'm getting thrown for a loop with "gatekeeping" because that's either a verb (e.g. "The dog is gatekeeping.") or an adjective (e.g. "The gatekeeping dog..."), but you're giving it a meaning that only works for a noun ("someone who doesn't have actual power but..."). Basically, I don't understand what you're trying to say, but what you're saying seems like something I'd like to understand.
From the regulation, Article 3:
1. An undertaking shall be designated as a gatekeeper if:
(a) it has a significant impact on the internal market;
(b) it provides a core platform service which is an important gateway for business users to reach end users; and
(c) it enjoys an entrenched and durable position, in its operations, or it is foreseeable that it will enjoy such a position in the near future.
2. An undertaking shall be presumed to satisfy the respective requirements in paragraph 1:
(a) as regards paragraph 1, point (a), where it achieves an annual Union turnover equal to or above EUR 7,5 billion in each of the last three financial years, or where its average market capitalisation or its equivalent fair market value amounted to at least EUR 75 billion in the last financial year, and it provides the same core platform service in at least three Member States;
(b) as regards paragraph 1, point (b), where it provides a core platform service that in the last financial year has at least 45 million monthly active end users established or located in the Union and at least 10 000 yearly active business users established in the Union, identified and calculated in accordance with the methodology and indicators set out in the Annex;
(c) as regards paragraph 1, point (c), where the thresholds in point (b) of this paragraph were met in each of the last three financial years.
https://eur-lex.europa.eu/legal-content/EN/TXT/HTML/?uri=CEL...
("core platform service" is explicitly defined to include social networking services)