Background pattern originally a PNG drawn in Paint.net
Source Firkin
It looks like a polished stone surface to me. Download it for free, as always.
Source V. Hartikainen
That’s what it is, a dark dot. Or sort of carbon looking.
Source Tsvetelin Nikolov
Prismatic Rounded Squares Grid 4 No Background
Source GDJ
Derived from a corner decoration itself found as a jpg on Pixabay.
Source Firkin
And some more testing, this time with Seamless Studio. It’s Robots FFS!
Source Seamless Studio
The classic 45-degree diagonal line pattern, done right.
Source Jorick van Hees
The image depicts polka dot seamless pattern.
Source Yamachem
From a tile that can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
The image is a seamless pattern of a fishnet.
Source Yamachem
A seamless paper background colored in pale yellow.
Source V. Hartikainen
A seamless pattern recreated from an image on Pixabay. It is reminiscent of parquet flooring and is formed from a square tile, which can be recovered in Inkscape by selecting the ungrouped rectangle and using shift-alt-I together.
Source Firkin
Remixed from a design seen in 'Burghley. The Life of William Cecil', William Charlton, 1857. The tile this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
From a drawing in 'Sun Pictures of the Norfolk Broads', Ernest Suffling, 1892.
Source Firkin
Brushed aluminum, in a bright gray version. Lovely 2X as well.
Source Andre Schouten
Not a pattern for fabrics, but one produced from a jpg of a stack of fabric items that was posted on Pixabay. The tile that this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
The texture of this background image has some similarities with leather, and it's colored in a dark brown color. So, if you are looking for a dark brown background image for your website, this may be an option for you.
Source V. Hartikainen
A white version of the very popular linen pattern.
Source Ant Ekşiler
Prismatic Groovy Concentric Background 2 No Black
Source GDJ
Similar to original, but without gaps in between the arrows. This seamless pattern was created from a rectangular tile. To get the tile, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
Remixed from a drawing in 'An Index to Deering's Nottinghamia Vetus et Nova', Rupert Chicken, 1899. The unit tile can be had by selecting the rectangle in Inkscape and using shift-alt-i
Source Firkin