Getting the wrong voltage while simulating a 555 timer
As far as I understand, the 555 timer is kind of a standard part.

Yes, definitely. That used to be called &quot;multi-sourcable&quot;.

Many manufacturers make it, but they all should match some pre-established specification.

Hopefully. They only do if there's actually an agreement between these manufacturers, which often isn't the case. It's not the case here: The original IC was just so simple and laxly specified (by modern standards) that it's easy to be &quot;compatible&quot; with the original specs, and that's kind of the common denominator. You still should check the datasheet of the exact 555 you're using if you're using it at high frequencies, high currents, low latencies...

However, there might be different families of 555 timers depending on the technology they use (CMOS, TTL...). Is this correct?

yes.

If so, my guess is that the simulator I'm using is simulating a TTL 555 timer, while the datasheet I was reading (the one above) speaks about a CMOS 555 timer.

That might well be the case.

That would explain the voltage drop I'm seeing (it makes sense that BJTs drop more voltage than CMOS, right?). Is this correct?

It would be a possible explanation.

Is that output voltage drop the drop you must expect from your Vcc? In other words, If my voltage supply is 5V I should expect 2.25 maximum, correct?

No, you must really read the datasheet of your chip to get that data.