cgbookcase.com
They provide high-quality PBR textures in the public domain with
resolutions going up to 8k (8.192 pixels):
1K: 1024 x 1024 pixels
2K: 2048 x 2048 pixels
4K: 4096 x 4096 pixels
8K: 8192 x 8192 pixels
Usually, textures in the PBR format feature a square size proportion for
all images. That helps with the tiling process of those textures. Most of
them are seamless. You can place them side by side with no visible
borders.
You can download most of those textures as a compacted zip file. After
extracting those files to your hard drive, you will get multiple image files
with a suffix identifying the map (Figure 5.16).
Figure 5.16 - PBR material files
The naming pattern for each texture map may change based on your
textures' source, but they will most likely follow the same types of
surfaces.