C4 model (see https://c4model.com/)
Arc42 (see https://arc42.org/)
After a quick read of the two I chose the C4 model because it felt familiar to me. Systems, containers, components and code is the way I think about software.
I chose to use https://www.draw.io/ with the C4 plugin. See the C4 model tooling section at https://c4model.com/#tooling
Here are the core diagrams (see https://c4model.com/#coreDiagrams) for the TexasToc application.