OmniGraffle single-handedly keeps me from switching to Linux. They have non-subscription pricing here:
https://store.omnigroup.com/omnigraffle?pk_vid=40876fd2b0ffb...
draw.io, aka https://www.diagrams.net
- Like OmniGraffle, but free, works great and open source! - You can use it online, saving to your cloud drive - Or you can install the desktop version
GitHub: https://github.com/jgraph/drawio