For example, can I use the same LLC to drive for Uber and for working on computer repairs?
Yes. There is no strict regulation of what kind of business can be operated out of a for profit entity in most jurisdictions, subject to some specific exceptions.
In certain regulated industries, e.g. banking, pubic utilities, alcohol industry firms, firearms sales and manufacturing firms, marijuana industries, law firms, firms of medical doctors, there are limits on the scope of what can be in a single entity. But, these are exceptions to a permissive general rule.