Low/Unstable FPS

FYI, if you have the 13" model, then there is a possibility that the internal hard drive SATA Cable is failing which is a very common problem with this specific model laptop especially when used with an SSD. Even the 15" model can be affected. Also, many of the Kingston SSDs these days are just low end models so their performance may not be as great as you think (it is very hard to get any technical specifications for their SSDs these days, but the few trusted reviewers out there who actually do more than say "SSDs are fast" have shown that the common/popular Kingston SSDs do not have any DRAM which will affect performance under random access conditions).

And you are correct, the problem may be with the OS, perhaps some issue with other third party software, or a system setting (OS or game), or even your network connection in addition to the other items already mentioned. You should also disconnect all external devices in case one of them is causing a problem.

The best way to eliminate possibilities is by performing a clean install of macOS by first erasing the whole physical drive in order to rebuild the file system & partition table. Then install macOS, but do not migrate or restore from a backup. Also only install the game and no other third party apps to see how it performs. This will be your best case scenario on how the game will work with your laptop with its current hardware configuration. At that point if you are still having problems, then it is either the hardware or a compatibility issue with the game (or a game bug) assuming you have turned down all the graphical settings possible. Game graphical settings are usually the only way to resolve the issues if everything else on the computer is Ok. Laptops (especially Apple laptops) are not really meant for gaming.

If the Steam CS:GO game forum community is unable to help, then you should contact Steam/Valve support directly for official assistance.

if would just stick with vsync if it was me the mac would still be at 60Hz vertical refresh so any frames higher than 60 would never be displayed anyway, also intel video cards are not really good for gaming (maybe excluding the new series they are introducing)

Are you running any anti-virus apps, cleaning apps, or third party security software that may be interfering with the normal operation of macOS? If so, then these types of apps can easily cause frame rate issues. Also, you may want to check your login items and quit them and all other open apps to free up both CPU & memory resources.

What graphical settings are you using? You may need to lower some of those graphical settings in order to get the game to run consistently. Shadows and anti-aliasing are two of the biggest graphical features that can destroy frame rates, plus you may need to lower the game's resolution and level of detail especially when using an Intel GPU considering Macs use a Retina display which has a high native resolution which may be beyond the capabilities of the Intel GPU depending on the other graphical settings.

Make sure macOS is completely up to date with the latest patches.

Also make sure that the game(s) are actually compatible with your hardware and your version of macOS. You may also want to check the Steam game forums to see if anyone else is reporting problems with CS:GO on the Mac.

What is the make & model of the SSD you are using?

Did you enable TRIM on the SSD? You can use the following Terminal command to enable TRIM on a third party SSD:

sudo  trimforce  enable

You will be prompted for your admin password, but nothing will appear on the screen as you type the password. Press the "Return" key to submit the password. I have read some posts on these forums where you may also need to run Disk Utility First Aid on the volume after you enable TRIM in order to force an immediate TRIM event to occur (this may need to be done from while booted into Recovery Mode using Command + R).

What is the exact model of your Mac and version of macOS? You can get this information by clicking the Apple menu and selecting "About This Mac".

Did you perform a clean install of macOS on the new SSD? Did you restore or migrate from an old system or a backup?