Unless you have been manually adding a contribution page to offline contributions, all of your online contributions will have a contribution page attached and none of your offline contributions will — with one exception, online recurring contributions beyond the first in the series won't always have a contribution page (not sure why).
So you could use SearchKit and search for contributions with recurring contribution is empty and the appropriate financial type. Then on the top right side of the results, add the contribution page column and the date received column. You could export these results and then make a chart out of the data.
If you wanted data for recurring contributions as well, I'm sure there is a way, but it's probably not important for what you're trying to do here.