A .db extension is not a format: if the first 16 bytes read 'SQLite format 3', the file is SQLite and any SQLite viewer opens it.
Use the sqlite3 shell for a quick look, DB Browser for SQLite or Letos for exploring, and a browser viewer only for non-sensitive files after checking it does not upload.
SQLiteStudio is now called Letos, and SQLite accepts text in integer columns, so check column types with typeof() before moving data to a stricter database.