It really depends on the position of the prospective employee.
An unemployed person who needs a job should theoretically spend their workday hours on recruitment efforts. The prevalence of fake jobs might affect which roles they apply for but not the total number of applications.
However for employed individuals seeking a promotion it can have a big impact. Is it worth spending many hours of your leisure time applying/interviewing for a job that pays 10% more, if the job has even a small likelihood of being fake? Probably not.
The 'well could be poisoned' for unemployed people as well. Applying to job adverts isn't the only type of recruitment efforts; there is also further education and tending to professional social networks - the unemployed individual could easily consider these more valuable than applying to probably fake job adverts. Ultimately, this still hurts both worker and employer, because it just delays gainful employment and hides information from the market.
An unemployed person who needs a job should theoretically spend their workday hours on recruitment efforts. The prevalence of fake jobs might affect which roles they apply for but not the total number of applications.
However for employed individuals seeking a promotion it can have a big impact. Is it worth spending many hours of your leisure time applying/interviewing for a job that pays 10% more, if the job has even a small likelihood of being fake? Probably not.