An open source project really shouldn't be something you need to "get off the ground." If it provides value then people will naturally use it.
Haha, have you tried that? I think in this day and age marketing is much needed activity even for open-source projects providing quality solutions to problems.
How do people know it exists to solve their problem? Even before LLMs it was hard to get through VC funded marketing by (commercial) competitors.
My first Open Source project easily got off the ground just by being listed in SourceForge.