Draw.io/ diagrams.net runs locally according to the documentation. E.g, you download the JavaScript app when visiting g the page and everything from there on is handled in the browser.
The thing with draw.io is that the pretty isometric views are only for AWS. I'd love to have something like https://www.cloudcraft.co/ that can be run locally for not cloud-based infraestructures.
Draw.io has been a blessing for me. I have used Visio in the past but I always experienced extreme frustration with that product. Over the past couple of years I have switched all my diagraming needs over to draw.io. It doesn’t seem targeted at any specific genre (network,flowchart, etc) but it is able to meet my needs. Unlike Visio it’s UI and operation is perfect for someone like me who just wants to draw and not spend a month learning a product. I have it deployed on prem as a server but it also has a locally installable application that doesn’t require a server. Kudos to the team that develops and maintains that project.
You can also install it in a rocker container.
https://github.com/jgraph/drawio