I posted and then deleted a comment as I was going to ask if you'd tried draw.io. Even when I worked in electrical design (infra+industrial), it was my go-to sketching tool to have open next to -CAD. What would you do to improve it for your use case, or are you lamenting that it isn't open source either?
It would be perfect if the symbols I wanted were already built in. There are some electrical symbols but they're very much circuit design focused whereas I'm looking for symbols such as these https://www.edrawmax.com/templates/1011842/
Definitely having built-in symbols for it would be nice. Regarding a titleblock, I found that custom data attributes on symbols and page backgrounds can accomplish as much as I would even need.
Create a page in your document called "Titleblock", format it and place dummy content if desired. For each "sheet", just select it from Page Background (you can set an image, URL, or another page in the diagram). For filling out information which varies, just have one titleblock symbol and add Placeholders for the custom data attributes which you add to it as well. (See: https://www.drawio.com/blog/placeholders) This is a common workflow in CAD as well just with different terms; i.e. a linked titleblock layout used for all sheets and a block inserted into the actual drawing with the attributes filled out.
