Excel 2016 sharepoint file still opens as readonly

You can use a library called ExcelLibrary. It's a free, open source library posted on Google Code:

ExcelLibrary

This looks to be a port of the PHP ExcelWriter that you mentioned above. It will not write to the new .xlsx format yet, but they are working on adding that functionality in.

It's very simple, small and easy to use. Plus it has a DataSetHelper that lets you use DataSets and DataTables to easily work with Excel data.

ExcelLibrary seems to still only work for the older Excel format (.xls files), but may be adding support in the future for newer 2007/2010 formats.

You can also use EPPlus, which works only for Excel 2007/2010 format files (.xlsx files). There's also NPOI which works with both.

There are a few known bugs with each library as noted in the comments. In all, EPPlus seems to be the best choice as time goes on. It seems to be more actively updated and documented as well.

Also, as noted by @АртёмЦарионов below, EPPlus has support for Pivot Tables and ExcelLibrary may have some support (Pivot table issue in ExcelLibrary)

Here are a couple links for quick reference:
ExcelLibrary - GNU Lesser GPL
EPPlus - GNU (LGPL) - No longer maintained
EPPlus 5 - Polyform Noncommercial - Starting May 2020
NPOI - Apache License

Here some example code for ExcelLibrary:

Here is an example taking data from a database and creating a workbook from it. Note that the ExcelLibrary code is the single line at the bottom:

//Create the data set and table
DataSet ds = new DataSet("New_DataSet");
DataTable dt = new DataTable("New_DataTable");

//Set the locale for each
ds.Locale = System.Threading.Thread.CurrentThread.CurrentCulture;
dt.Locale = System.Threading.Thread.CurrentThread.CurrentCulture;

//Open a DB connection (in this example with OleDB)
OleDbConnection con = new OleDbConnection(dbConnectionString);
con.Open();

//Create a query and fill the data table with the data from the DB
string sql = "SELECT Whatever FROM MyDBTable;";
OleDbCommand cmd = new OleDbCommand(sql, con);
OleDbDataAdapter adptr = new OleDbDataAdapter();

adptr.SelectCommand = cmd;
adptr.Fill(dt);
con.Close();

//Add the table to the data set
ds.Tables.Add(dt);

//Here's the easy part. Create the Excel worksheet from the data set
ExcelLibrary.DataSetHelper.CreateWorkbook("MyExcelFile.xls", ds);

Creating the Excel file is as easy as that. You can also manually create Excel files, but the above functionality is what really impressed me.

I have been trying to fix the same problem for my files, and eventually did! So I felt that I could maybe let others know. And this old-ish thread came up near the top of my google search.

What fixed it for me was to edit the link.

from: https://Company.sharepoint.com/:x:/r/teams/TeamNo/Shared%20Documents/Example/CoolFolder/TheBestExcelFile.xlsm

To: https://Company.sharepoint.com/teams/TeamNo/Shared%20Documents/Example/CoolFolder/TheBestExcelFile.xlsm

Note that I only used replace to get rid of :x:/r/. I feel like I should have noticed this before but I didn't and no amount of meddling with the Workbook.Open parameters got me anywhere. It just seems odd that the default link copy thing gives you one with special commands in it. For our company most folders have spaces so the link has tons of "%20" in there so I simply read over the ":x:/r/".

Hope it helps someone.

Just for clarity, try this:

Sub Example()

'1.) Get filepath from somewhere
FilePath = Replace("https://Company.sharepoint.com/:x:/r/teams/TeamNo/Shared%20Documents/Example/CoolFolder/TheBestExcelFile.xlsm", ":x:/r/", "")

'2.) Open the file
Set StatisticsFile = Workbooks.Open(FileName:=FilePath, Password:="123")

'3.) Do things

'4.) Close the Sheet, save the changes. I simply like it this way, could be done in a single line.
StatisticsFile.Save
StatisticsFile.Close savechanges:=False

End Sub

I noticed this solution because I could still save the .xlsx file manually with the same name if I navigated to SaveAs. So if you guys can still do that after opening the file via macro, try a similar solution.