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I find it typically said that the maximum Cat6a cable distance is 100m for 10GBASE-T.

But often for a 10GBASE-T SFP+ transceiver, the product is said to support a maximum of 30m. For example: Cisco SFP-10G-T-X

What does the 30m really mean? Does it mean that using the transceiver actually reduces the maximum cable length by so much, perhaps by introducing signal loss somehow? Or perhaps the transceiver sends a lower-power signal than a built-in RJ45 port and so cannot cover as long a distance?

For using cables longer than 30m for 10GBASE-T, is it better to use built-in RJ45 ports instead of SFP+ tranceivers?

EDIT: Removed the incorrect part about Cat8.

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    I find it typically said that the maximum Cat6a cable distance is 100m for 10GBASE-T (longer with higher categories like Cat8). That is incorrect. The defined categories are 3, 5e, 6, 6a and 8. All are UTP for 100 meters, except Category-8, which is to support 25GBase-T and 40GBaset-T, up to 24 m horizontal, and 30 m channel length, much shorter than the other categories. It will handle 2000 MHz, and it is only shielded cable, the first non-UTP cable category recognized. There are three variations, one doesn't fit the standard 8P8C. Longer Category-8 cabling is incorrectly installed.
    – Ron Maupin ♦
    Commented Jul 9, 2022 at 17:18

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Yes, the transceiver actually reduces the maximum cable length.

This reduction is due to the maximum power draw of an SFP+ module of 2 Watt and considerable power requirements for 10GBASE-T because of the frequency-dependent attenuation in copper. (Depending on the host device, the limit may also be 1 or 1.5 W, which usually means no support for 10GBASE-T.)

However, there are special 3rd-party SFP+ modules that claim to reach 80 or even 100 m. You might want to verify the compatibility and the capabilities with the vendor.

If those modules can't meet your requirements you might want to consider 10GBASE-SR over multi-mode fiber which uses much less power and reaches 300 m over OM3.

The only other solution is to use a switch with native 10GBASE-T ports - these support the standard reach of 100 m over Cat 6A cable.

And the standard does not specify any longer reach with better cabling like Cat 8.

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