It can handle no connection quite well, but unstable internet is really a PITA - commands and applications lag randomly when launching etc... It took me some time to troubleshoot why suddenly ma MacOS was almost unusable and this was the culprit.
Like plugging a device that will be seen as network card and responding to certain api requests to trick whatever service calls them?
You actually want the opposite, to make it think it's not connected to the internet. In other words, a network connection blockers such as Little Snitch.
That will result in almost unusable system.
I used a similar method to simulate running our software on a government network when I worked in defense.
Timeouts and packets dropping all over the place. Government work sucks.
And the most painful thing is that Macbooks don't have eSIM/cellular so you have to use iPhone with its small-ish antenna. So you have a MBP and your system is barely usable and next to you is your colleague, using DELL with built-in LTE and 4 large antennas behind its display doing over 70Mbps with a sh*t-eating grin asking you if you want to use his computer :-D
The problem is responding to those API requests in a way that the program will accept - if it's just a simple PING, no issue, but if there's any sort of more advanced encryption, handshaking or license checking/exchange going on, you'll need to reverse engineer the algorithm. Some simple versions of that you can just record once and "replay", but most will at least have a timestamp hashed in.
(super rough, lay-man's understanding of the issue - sorry for any inaccuracies)
There are several other methods that I've seen but they are not bulletproof: - talking directly to hardcoded DNS such as 8.8.8.8 - hardcoding IP addresses into SW - Checking for some obscure header as a part of client/server identification
Source: typing this from an older ("late 2009") iMac running Linux
I want to have modern peripherals and experience such as 4k display, USB-C, reasonably fast wifi/bluetooth. I don't really have a need for CD-ROM, firewire and IR port...
And believe me, I tried to run Linux on 2018/2019 MBP. Apple really really tries to makes that as painful as possible. Most of the things are behind T2 (including keyboard for example) and since there is virtually no documentation you have to rely on reverse engineering efforts of few talented individuals. Also there are things that just plain don't work such as resuming from sleep (the graphics MUX gets all confused and the driver will not re-configure it for some reason) etc... Basically nice for playing around, not good enough for running as a main device.