Anything man made is venerable. So yes, the internet can be degraded or put out of commission. It takes constant maintenance, upgrades etc now to keep it functioning . We all have in-counter outages from time to time.
How? Terrorist, EMP/Solar Flare, acts from a hostile government (virus) or EMP detonation?
It would surely cause mass panic, loss of communication, hospitals will practically be useless due to dependence on circuit boards (medical equipment) , law enforcement (no radios), all modern vehicles will cease to operate , no water, resuppply of food stock, no pumping of fuel from tanks, The list is endless. Everything today requires computers ie circuits and the internet to transfer data.
If you can not operate a machine or place an order or communicate via a circuit/computer we are back in the Middle Ages.
A fortnight interruption wound exhaust all food and stored water, consume and medical supplies, have massive looting and riots, increase homicides, a die off of the population depending on constant medical care and treatment, not to mention the doomsdayers committing suicide etc.
Imagine the catastrophic effect beyond a fortnight. The rampant rise in crime, gang violence, neighbor against neighbor for resources , cities spilling out into suburbs etc. Masses of people without basic skills of hunting, trapping, horticulture etc . Masses without stored resources, only what’s in their pantry.....