We don't currently index works from institutional repositories, but instead if we have record of a work from another source (e.g., Crossref, DataCite, HAL, PubMed, etc), we scan repositories for open access versions of those works.
If we find an OA version of that work, we link it to the main work record and the repository could get included as a source of that version, hence why you might sometimes see your repository as a source for the work even though we don't index works from your repository.
Finally, it is also possible that we inherited records before 2022 from Microsoft Academic Graph who in some cases minted work records from institutional repositories, though not in a systematic way.
If you want to see if your repository is on the list we look in for open access versions of works or add your repository to that list, go here: https://unpaywall.org/sources
In Spring 2025, we'll be piloting the complete index of some repositories to be able to start minting new records from repositories. If you would like to collaborate with us and/or have your repository considered for indexing in the first round of work, please fill out this google form: Registering Repositories with OpenAlex - Google Forms