Imagine having hundreds of journal lines to import that need posting across multiple legal entities. Now imagine having to log into each legal entity one-by-one, to post the journal lines for each entity.
Clearly that is unacceptable for anything over a couple of lines and/or legal entities!
Until relatively recently, it was only possible to create a Global general journal, i.e. a General journal for another legal entity, within the current/active legal entity.
A relatively new piece of functionality now allows you to post Global general journals in batch. Check out the relevant entry in the Feature management workspace:

How does it work?
We begin in General ledger > General journals > Global general journals. From there, choose New journal, select the company you’re looking to post to, and the journal name (i.e. type).
In this screenshot, we’re currently in the GBSI legal entity, creating a Global general journal for USMF, with the journal name “General”:

The journal will be numbered with the next value in the series from the USMF “General” journal number sequence, not any number sequence from GBSI. Good start.
You can then populate the journal exactly as you would a normal general journal, either single entry (with offset) or double entry, taking full advantage of the ability in D365 F&O to select different account types (Ledger, Customer, Supplier, Project, Fixed assets, or Bank) and access/use the data from the corresponding legal entity:

With your Global general journal(s) created, it’s now time to post them, in batch, still without changing legal entity. This is the critical functionality introduced in release 10.0.34:

Posting your Global general journal creates a batch job in each corresponding legal entity to finalise the posting of the journal there. Result!
N.B. If the Post button is greyed out, it’s because the feature isn’t enabled in your environment – check back to the start of this post!
But what about the hundreds of lines…?
In real terms, you probably don’t want to be doing this manually. I’d conject that it’s more likely that you’re trying to post a large volume of lines, so you will be better off using the Open lines in Excel feature:

It occurs to me – and I haven’t had the chance to try this – that it might be possible to build an Excel template that populates multiple journal batches simultaneously – that experiment will have to be for another day!
What does it not do?
It is important to point out that this functionality does not permit users to post a journal batch with multiple lines for different legal entities (aka companies). This requires intercompany posting configuration, which whilst perfectly achievable, is not the outcome we’re seeking to achieve here.
In the screenshot below, you see lines for USMF (and GBSI) in a GBSI-linked Global general journal. This will not post (without appropriate intercompany configuration):

It is also well worth mentioning that the ability to create journals and post to other legal entities is dependent on the user having the relevant permissions in those legal entities.