Learn German: Wir eröffnen die Versammlung der Eigentümer. - We are opening the assembly of the owners.

Öffnen means to physically open a tangible object, like a door, a window, or a box. Eröffnen is used for officially starting or inaugurating an event, process, or institution, such as an assembly (Versammlung), a meeting, or a bank account.

How does this active sentence relate to the perspective shifts we are learning in this lesson?

Here, the subject (wir) actively performs the transitive action of opening the assembly. If you want to shift the perspective to the assembly itself as an ongoing state—similar to how you use intransitive support verbs like zur Verfügung stehen—you would use the statal passive (Zustandspassiv): Die Versammlung ist eröffnet (The assembly is open).

Is der Eigentümer singular or plural in this sentence?

It is plural. Der is the genitive plural article here, meaning "of the owners". If it were singular masculine ("of the owner"), the phrase would be des Eigentümers, requiring both the article des and an added -s at the end of the noun.

Could we use Besitzer instead of Eigentümer for "owners"?