My advice would be to make use of pre-launch platforms such as https://microlaunch.net or product hunt and other organic ways to gain traffic. Meanwhile, make sure your funnels converts, then think about Ads later on.

There is no solution that fits all. Depends of your target audience and where they operate.

Audience is on Twitter/X ? Build in public and post regularly about your work. Audience is on facebook ? Targeted Ads may work for you Audience is a set of professionals ? Target forum or places they go

Disclaimer: I'm not an expert in marketing either :)

Reddit is a really great way right now, due to the boost to Reddits rankings on Google you can find old Reddit threads that still allow comments in the top 5 on Google with very high traffic keywords.

Newsletters and directories like https://microstartups.co/

Invest in SEO.

Maybe too abstract, so here is a piece of actionable advice:

99% of SEO is to publish interesting content for your target audience.

Read Alex Hormozi's "$100m Leads"