When I did my last job search in 2022, linkedin gave me > 100k results from a "remote senior software engineer" query, and there weren't good filters to narrow the results down. Other sites were too niche.
It's tough to start a job board from scratch. It's the chicken and egg problem for two sided marketplaces: no jobs, which means no traffic, which means no one wants to post jobs, etc. I decided to aggregate from some other sites to start (allowed via their terms).
Let me know what you think! Will answer any question.