Literally, bitcoin is money. Therefore you can get bitcoins in the same way you earn money. Any work or job is useful to earn some dollars that you can change for bitcoins later.
That's the point. Any ways that earn money can be the ones to earn bitcoins.
But in the earning of bitcoin we have to keep in mind that nowadays we cannot earn bitcoin in offline work/job but we can earn only on internet and in the activities which can be done on internet. On some places shops are also earning bitcoin.
Yes I would agree with that. In response to the OP though like everyone else has said asking how many ways to earn bitcoin is like asking how many different jobs there are that one could do. There are an infinite number of jobs and ways to earn money. They each have different risks and gains and you have to decide which is best for you. There is no one job fits all just like there is not one for fiat currency either.