I have a blue plate/brick , that is 6x6 it has studs in the middle that are 4x4 with the four corners as holes it has raised sides. Can anyone help please.
The number on the back (88409) is just an alternative ID of the "Tile 2 x 2 with Groove". The other known IDs of the same (undecorated) tile are 3068, 1136 or 78814. This decorated tile appears in one set only, hence the high price.
And if you didn't think of the keyword. You know it's a decorated tile and 2x2 in size and the color. Search for 'tile decorated "2x2"' and filter that result on the correct color
Comments
First searched for "6 x 6" (with the quotes) and then selected the color, leaving only 48 options
https://www.brickowl.com/catalog/lego-tile-2-x-2-with-chest-x-ray-decoration-with-groove-3068-99823
You know it's a decorated tile and 2x2 in size and the color.
Search for 'tile decorated "2x2"' and filter that result on the correct color