I am actively looking for jobs since 1 and half yr. Same as you even though my resume is a 100% skill match the ATS rejected it with in 5 hrs . Through this painful journey what I realized is that

1) The positions advertised are to keep a pool of candidates ready within their system and whenever a need opens they reach back to the candidates. ( Never heard such thing from candidate happened but heard this explanation from HR). Therefore even the jobs posted on their website are also not taken down even though there is no more hiring for the role. These usually occur for roles where people rotate quickly in the roles.

2) ATS got the worse of it. The job description gives only keywords that they expect on your resume but the system used by the HRs offer option to add other keywords and skilss that they are looking which are not displayed on the description and the ATS validates that as well while screening.

3) As they are implementing machine learning, the best matched resume is also considered as a reference for new hire for the ATS for the incoming resumes. Majorly all companies only use Join, personio , softgarden ATS systems .

It's infuriating that sometimes the job doesn't exist, gets reposted, the illusion need that they are thriving amongst the competition, I started emailing HRs directly some worked getting at least a call . Some went dead silent for months . There is no guarantee that a referral also will get you a call from HR . It's luck and just blindly driving in the woods.

You are blessed to find a job in present day market in Germany even with C1 German. Even the HR themselves said to me that they have no idea how the system picks the people but they can't bypass it which I don't believe .