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
A light gray fabric pattern with faded vertical stripes.
Source V. Hartikainen
A background tile for web with abstract repeating texture of dark "stone wall".
Source V. Hartikainen
Kaleidoscope Prismatic Abstract No Background
Source GDJ
Thin lines, noise and texture creates this crisp dark denim pattern.
Source Marco Slooten
ZeroCC tileable wood boards texture, photographed and made by me. CC0
Source Sojan Janso
Prismatic Abstract Geometric Background 2
Source GDJ
Submitted as a black pattern, I made it light and a few steps more subtle.
Source Andy
And some more testing, this time with Seamless Studio. It’s Robots FFS!
Source Seamless Studio
From a drawing in 'Sun Pictures of the Norfolk Broads', Ernest Suffling, 1892.
Source Firkin
A seamless pattern based on a rectangular tile that can be retrieved in Inkscape by selecting the rectangle and using shift-alt-i.
Source Firkin
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
Found on the ground in french cafe in kunming, Yunnan, china
Source Rejon
Same classic 45-degree pattern, dark version.
Source Luke McDonald
A pale yellow background pattern with vertical stripes. The stripes are partially faded. I think this background image turned out pretty well, especially those faded stripes.
Source V. Hartikainen
White little knobs, coming in at 10x10px. Sweet!
Source Amos
A background formed from an image of an old tile on the New York Metropolitan Museum of Art website. To get the base tile, select the rectangle in Inkscape and use shift-alt-i.
Source Firkin