Using Pages/Keynote v11.2 on macOS 12.0.1, I can get table content from Pages into Keynote in two different ways.
You can select, then copy to the clipboard, the table from Pages. By issuing just a Paste in Keynote, the Pages table is recreated there without cell content attribute changes. Paste and Match Style will deposit the table, but with bold and larger cell contents.
You can create a new table in Keynote. Then, select the table cells in the Pages table and copy that selection to the clipboard. Back in Keynote, click once to select the first cell in that table, and then paste. The Pages selection will then populate the Keynote table, expanding it if necessary to accommodate the selection range.