If you export the Posted project transactions report from D365 for further analysis, it requires a bit of formatting to get it in a sortable, summarizable format. Here are the directions to do this once you've exported the report to Excel from D365. These directions are also pretty valid for most any detail report export from D365 that you'll need to massage in Excel.
Open the exported report.
Click on the Table Design tab, then choose "Convert to Range"
When asked if you want to convert the table, click "Yes"
Now you can add the subtotals.
Click the "Data" tab, and click the "Subtotal" button
This will open the Subtotal menu.
For "At each change in" choose "Asset". (If you want to subtotal by something else like Financial dimensions, you would pick what you want there)
For "Use function" choose "Sum"
For "Add subtotal to" choose "Total cost amount" (If you want to include a subtotal for other columns, you can check them as well.
Click the "OK" button.
This part may take a bit depending on how much data you are reporting on, but it should show you the lines, with subtotals below each Asset.
If you want to cut some of the clutter, you can select the "2" in the top-left of the data to just show the subtotals:
This will hide the lines and only show the subtotals.
Press the "3" in the same area to show the lines again.
For readability, it might be worth dragging the Total cost amount next to the Asset column in D365 before you export it.