I don't have a great filing system, but it has been sufficient so far: have all documents in the same folder, put their respective date in the filename together

I don't have a great filing system, but it has been sufficient so far: have all documents in the same folder, put their respective date in the filename together with some tags ("yymmdd_name_and_tags.pdf"), and convert scans to searchable PDFs with "ocrmypdf" on Linux. The date and comprehensive filename is often enough to find a document, but additionally I can do a "full text search" on all documents with the text layer that is put onto scans by the OCR.