I would like to get your opinion and perhaps enroll in some vocal lessons. I do mostly rock and roll music (middle aged hobbyist guitar player) and would describe myself as being ‘almost’ able to sing. I can often produce vocals that are non-offensive, but none that are really good. I do not want to pursue futility and don’t know enough about vocal music to know if one can actually ‘learn’ to sing or if it’s something you are just born with and either have it or don’t. If there is any potential I would certainly pursue it.

Hello and thanks for writing with your question.
Singing is a skill, just like anything else. Nobody is born being especially good at anything. They may have a strong inclination towards some activity and then they work at it to get good. The same applies to singing. Some people may be inclined to sing more than another person. But all this means is they will be more willing to put in the work necessary to develop skill at it. If you are able to sing at a “non-offensive” level without any training then it is very likely that you have potential that can be developed. The great majority of people who sing just started out with a desire to sing, which led them to learn about the voice and how it works. They were not particularly good before they learned to develop their skill. The only way to really find out is to meet with someone with experience who can assess you accurately.