You are expected to do a job that does not involve computers. Physical labor, cooking, stocking a store, janitor, farming, etc.
Carpentry. Cooking. Child care. Road paving. Picture framing. Pottery. Farm equipment driving. Teaching tennis. ...
Having no access at all to a computer is a rare case. Most cases, felons are not permitted to have any *unsupervised* access to computers or internet. This is checked on and enforced by a parole officer, and is only enforceable for the period of parole or probation as defined by the court judgement.
They are allowed to use a computer at work, as long as the employer can monitor and provide logs to law enforcement as needed. Same for public library access. Access has to be login restricted and browsing history and usage has to be logged and reported.
A personal home computer or smartphone is a no go. An exception might be made for a computer at home, so long as the parole officer or other law enforcement is satisfied that it cannot connect to the internet and it can and will be taken at any time for a forensic inspection.
As a side note - I wonder if those same people that are sentenced to not use a computer are able to use a smart phone? I mean, if you get right down to it a computer could be defined as a lot of different things that people use everyday without realizing (cash registers, ATM, are a couple I can think of quickly).
This has happened to hackers convicted before, some find other things to do or end up hiring programmers who can get near computers to implement their designs. Some become security consultants.
By doing something which doesn't use a computer, which is still very possible, but you are right to recognize that it is increasingly limiting. This has led some to call for an end to this sort of sentence as being inhumane.