There are only two demat account issuers (depositories) in the country - NSDL and CDSL.
The frontend that consumers (aka you) touch are all depository participants (DP) referred by you as apps - eg Zerodha, Kuvera, Kotak Sec, ICICI Sec, etc.
DPs are your gateway into investments but ultimately everything resides with either NSDL / CDSL, so your question is moot.
Choose a single app that is cost optimised for your use case (investments / trading) and has the functionality that you need. All of them are very similar with very little differentiation.
More than 1 account isn't needed for a majority of people. The only ones who have more than one investment app / account split those by use case. Investments in one and trading in another.
Happy investing!