There is unlimited length restriction in the HDMI standard. In general, it is supposed to be 15 meters with a metal cable.
Commercially available cables are mostly up to 15 m.
It seems that it is sold until about 20 m when you search.
However, various extender products are available to sale and it is possible to extend up to 100 m.
The following is an extension using a coaxial cable that makes it possible to extend up to 120 m.
