Comment by runnerup

This tool helped me a lot over the past decade, and I still jump to it for simple circuit simulation at work (I do embedded firmware development, but lots and lots of oscilloscope/multimeter/logic analyzer use to troubleshoot and validate)

https://www.falstad.com/circuit/

This tool is fast enough to whip things up during a troubleshooting session alongside Electrical Engineers, and thorough "enough" to be used as a reasonable reference by the Electrical Engineers.