Does it really run at 40Gbps?

The adapter is rated for 40Gbps, but the result depends on both cables you join. Two certified 40Gbps cables in a short run are the best case. Longer combined runs or weaker cables will fall short.

Can it carry 240W charging?

It is rated for 240W at 50V, which covers the highest USB-C Power Delivery tier. The charger, cable and laptop must all support that level too.

Will it work with a USB-C monitor?

Yes, it passes video and audio, rated for 8K at 60Hz and 4K at 120Hz. The source, cable and display need to support the same mode.

Is it the same on both ends?

Yes. It is a female-to-female coupler, so both ends accept a USB-C plug. It does not convert USB-C to USB-A or anything else.

Does it work with Thunderbolt?

It should pass Thunderbolt 3 and 4 signals when both cables are Thunderbolt-rated. It is a passive coupler, so it adds no Thunderbolt features of its own.