What software to use to maintain a customer database?

Question

Knowledge base

Tell me software for maintaining an unusual customer base with the following features.
1. Required fields to fill in: full name, position, organization, organization address, phone number, mail, and 7 more fields (I can’t write about them). Ideally, you can add / select the number of fields yourself.
2. Ability to attach files to a specific person.
3. For android and linux. Optional, but as a bonus, Windows and iPhones.
4. Completely free.
5. Locally installed software, not a web application.
6. Built-in search.
This is the main thing. Of the non-essential wishes: the ability to backup or synchronize. Now the entire database is in an excel file, there are about 2000 records. 7 people work with it and everyone is ready for the fact that manual input from Excel to the program may be required.

Answer 1

no
because of this
but you can tinker with this
https://github.com/tfreier/desktop-crm

Answer 2

cooler access only access

Answer 3

If you throw out one of the items 3, 4 and 5, then there will be three options.
But none of them fit the same criteria.