Should we somehow enforce rules of this slack if they are being purposefully ignored? e.g. we have this

Job ads should have a specific description of what is expected, location, remote/on-site, and salary range

in #hiring, but there are some posts there authors of which decline to give salary range even in PM.

I don’t really have a strong opinion if it should be treated as a rule, or as a recommendation. For remote work salary range is often pointless.

How is that pointless? Remote work is still work and needs to be remunerated, so there is still a salary which is falling into some range, remote workers are interested in what that range is, same as on-site workers. I don't see any difference here from prospective employee's point of view. The only thing that could sometimes differ would be how the range is expressed (yearly, monthly or hourly), remote work is remunerated based on hourly rate more often than on-site work, the rest is the same.

Yes, of course, but from country to country it is so different, and also depends on some legal regulations, job market, etc. But I’m no expert in this.

Yup, for international people usually state gross salary range, that gives a potential employee at least a rough idea of what to expect, net salary will depend on all those factors you've mentioned, but gross doesn't.