VAC / Overwatch / Untrusted
#[1] Basic information about the VAC system
the system is automatic and infallible. This means that if you have VAC on your steam account, you have used third-party programs.
This lock cannot be removed.
Once you receive this lock, you cannot sell / buy / exchange CS:GO items.
VAC is a system whose database of third-party programs is updated on a regular basis and it is impossible to predict or tell when the last VAC update was.
CS:GO Update is a game update, not a VAC system.
This blockade may be delayed. The point is that if you used a program that was already in the VAC database (detectable) then the blockage can come up to 2 weeks.
Checking takes place on Valve servers where signatures, MD5 sums of files, etc. are checked.
#[2] Overwatch, VAC Ban, Untrusted
VAC Ban
You get a lock when you use detectable software through a VAC system.
After receiving such a blockade in the game we see a rectangle with the inscription "VAC (Valve Anti-Cheat)"
and on the profile "1 VAC ban on record"

Overwatch
This blockade is granted by "Supervision" here it is not that the VAC system has detected third programs with us
but that people watching our game issued a verdict that we used third programs.
This blockade is also related to the fact that we cannot sell / buy / exchange CS:GO items.
This blockade will not be removed if you have used any third-party programs, but there are cases when "Supervision" is mistaken.
After receiving such a blockade in the game we see a rectangle with the inscription "Global time penalty".
and on the profile "1 game ban on record"

Untrusted
This blockade is usually granted for out-of-date support using old memory addresses. Malfunctioning aimbot, most often it is a programmer's error.
Some functions for which we can get a untrusted, e.g. Anti-Aim, NoSpread ..
Some time after receiving the lock, a message from VAC will appear on the Steam profile.
It is enough from 5-20 minutes to play on a poorly made cheat to receive such a blockade.
The block is granted automatically.
After receiving such a blockade in the game we see a rectangle with the inscription "Global time penalty".
#[3] Other useful information
VAC blockade is not the same as Overwatch, the difference between them is that if you got VAC, the software you used is detectable, but when you get OV you have been convicted by "Supervision" so on your demo you could see cheats such as wh / aim / bh etc.
Update CS:GO is not a VAC update. So after updating the game (small, one that doesn't change offsets / pointers) you can keep playing if the program is still undetectable by the VAC system. Just because the game has been updated doesn't mean that the VAC system either. As I wrote, the VAC system is updated on a regular basis and it is impossible to say when it was.
Remember that VAC ban may be delayed, so use public cheat for a maximum of 3 days. The more people use a given cheat, the faster it will be detected, so it's best not to use very popular public cheat, but when you have to, I recommend max 1 day.
Great contribution. A lot of people still can't see the difference between those.
What I think is wrong is that you have typed that VAC's last update can't be known, this is half-wrong. The Anticheat itself rarely gets updated. But if it gets updated it comes with a Steam Client Update. So if you are reversing these each Update you might see changes to the VAC itself. But most likely not really.
What you can't know about the VAC is what Signatures got added to their database. At least I haven't seen any Network Reversal / Hacking in that direction. That's the point where you are right when you mentioned "it's impossible to predict VAC updates" or how the line was. But I think you meant it like that. So, meh. xd
Wait a Minute. What is this Signature? You actually just stole my hand-made image!
So you can be VAC banned as long as you have the cheat in your PC(which is in VAC list)? Even though you did not activate / use it, right?
And hence, if you are using a cheat all along safe, and if suddenly there is a steam update, it might be risky cos VAC might be updated with new data?