I've just had the complete opposite experience and same with a few colleagues
We get told of a merger, they do the "Don't hope for an email," thing that day/week and then axe the fuck outta people
Maybe we've just got into a basket where that happened, but I've legit never seen that sort of "We're canning you in ummm, like 3 months," shit
The only thing I can't really account for is the pandemic and how each company will handle that; shit company I'm working for now fired a dude right as the US closed up shop
Odd question; might you guys be 35+?
Not quite there but almost. The only time I've seen a "clean out your desk, you're gone" along with the guy's credentials being completely frozen and locked out that day was in a gross misconduct case (snapped with his boss and was very obviously trying to physically fight him) which are obviously rare in most places.
In some cases you'll be put on "gardening leave" which just means you're gone but you're still technically an employee until the agreed upon date. That's either reserved for employees who might have the potential to try something or if the news gets out and they want to save someone the embarrassment.
It's also worth pointing out that I'm from a country that mandates redundancy payouts for most employees (unless you have been there a very short period of time) and if you don't get some from the company, you get some from the state. However, if you do some crazy shit like fucking up an IT system, deleting files or other retaliation your redundancy suddenly becomes a dismissal for gross misconduct and you are losing out on potentially large sums of money.
I was once "given the responsibilities" of some of the work of a guy who was being shown the door. His handover was to forward me a short word doc and then to put his feet up on his desk for a month while winding down the clock. Not malicious but probably not what the company had envisaged but I couldn't blame the guy.