Multiplatform conference system with invitation support for external

In the company where we work, we have been struggling for years to find a conference system that works for demonstrations, previews of meetings, etc.
The most important characteristics required are:

  1. Audio
  2. Share screen
  3. Ability to invite external people who do not have a company account such as AD or similar
  4. Multiplatform (Windows, MacOS and Linux)

We have tried:

  • WebEx (It seems that they are no longer interested in supporting Linux)
  • Hangouts (the best alternative so far, but limited users and the quality too variable)
  • Skype for companies (not compatible with Linux)

I have looked in

  • Slack – but lack the required feature 3
  • Discord – also lacks the required feature 3