Open the board, click the three dot menu at the top right, and choose "Export board to Excel". That is the path monday.com's support centre documents. On some accounts the option sits under an "Import / Export" submenu inside that same three dot menu, so if you do not see it at the top level, look one step down.
A small dialog appears with checkboxes. The two that matter are the one for including updates and the one for including subitems. They are not ticked for you. An admin who clicks straight through gets a clean spreadsheet with no comments and no subitem rows, and often does not notice until weeks later. Tick them.
The file downloads as .xlsx. Groups become a column or a row break depending on your board structure, items become rows, and each board column becomes a spreadsheet column with its display value.
Do this before you click export
Switch to the main table view and clear every filter first. A board view with a filter applied can export only the filtered rows, which is the quietest way to lose data in the entire process. Also check whether anyone has hidden columns in that view. Hidden columns have a habit of being the ones holding client IDs or invoice numbers.
Then check the row count. Count the items on the board, count the rows in the file, and make sure they match. If your board has 4,000 items and the spreadsheet has 4,000 rows plus a header, you are fine. If it has fewer, something filtered it.
What the Excel export does well
Text, numbers, dates, status labels, people names, tags and checkboxes all land fine. Long text columns come across with their content intact. Item names and group names are reliable. For a board that is genuinely a list of things with attributes, the Excel export is honestly all you need, and you can stop reading at this section.
What it does badly
People columns export the person's display name, not their email address. That matters because display names are not unique and emails are. When you load that spreadsheet into anything else, you will be matching "Dave S." against a user list by hand.
Timeline columns squash two dates into one cell. Time tracking columns give you a total, not the individual start and stop sessions. Status columns give you the label text and lose the colour and the index behind it, which is fine until you discover two boards used the same label for different meanings.
And item IDs. Check your file for them. The item ID is the number monday.com uses internally to identify each row, and it is the thread that ties an item to its subitems, its updates, its files and its links to other boards. Without IDs you have a spreadsheet of names, and names are not a key.