It's FOSS - https://itsfoss.com/visio-alternatives-linux/
Brief: If you are looking for a good Visio viewer in Linux, here are some alternatives to Microsoft Visio that you can use in Linux.
Microsoft Visio is a great tool for creating or generating mission-critical diagrams and vector representations. While it may be a good tool for making floor plans or other kinds of diagrams – it is neither free nor open source.
Moreover, Microsoft Visio is not a standalone product. It comes bundled with Microsoft Office. We have already seen open source alternatives to MS Office in the past. Today we’ll see what tools you can use in