Is it appropriate if my former advisor is editor of a journal I submit to?

I don't see any conflict of interest on your side preventing you from submitting to this journal. You can only assume that your former advisor has good ethics and will abstain from handling this manuscript.

Consider the consequences if someone you had a close working relationship with being on the editorial board would prevent you from submitting to a journal: many senior scientists could not submit to any journal in their field.

You have no ethical conflict whatever. As you say, the advisor might need to not comment on your submission. However, it is the reviewers, not the editors who will be judging the quality of the submission, with the editors making only final selections.

If there are any conflicts they are for other people and for them to resolve.

I doubt that this is uncommon, especially for specialized journals. They likely have seen the situation many times and have appropriate procedures for handling it.