They said they used holding companies.

If you are just paying a couple of $100 a month for app related stuff you can just use a new bank if you want and just transfer the amount needed each month. Opening accounts is something banks really like when you do so its usually not hard.

Don't you have to name the account after a real or legal person?

Depends on the country. A well regulated bank has to know who the real or legal person behind the account is, but that doesn't necessarily mean the name of the bank account has to correspond to the name on a birth certificate. It's the business of the state to make sure they can tax you, but it isn't the business of the state to make sure Google can ban you.

It also depends on whether your company legally resides in the US or not. And also where the HQ is located (as that's the legal baseline for taxes in Ireland).

Most of those mega companies probably are not even paying taxes in the US, due to them having their legal residence in a postbox office in Dublin.

In addition to my initial comment: Most banks that offer enterprise/business bank accounts have a feature to split up accounting so that you can manage the financials of teams and suborganizations in a separate manner which eases up filing tax reports, too. I know that this is the case in Europe, but dunno anything about the banking system in the US.

I think you are looking for the term 'legal entity' instead of 'legal person'.

No, “legal person” (as opposed to “natural person”) is a real term.

Many fintech banks do give you the option to open up separate accounts with individual bank account numbers quickly and hassle-free, e.g. bunq.

I too am trying to work that one out. My guess is that they used DBAs, each with a separate bank account.