There are all sorts of pre-existing users in the 6 GHz, so when the FCC (for one) approved its use for Wifi, it included restrictions. Some already-licensed stuff:

* Sub-band U-NII-5, 5.925-6.425: Fixed Microwave, FSS (uplinks)

* U-NII-6, 6.425-6.525: Broadcast Auxiliary Service, Cable Television Relay Service, FSS (uplinks)

* etc

Via: https://docs.fcc.gov/public/attachments/DOC-363490A1.pdf

Some details for approval:

> Standard Power is the only access class that supports Wi-Fi 6E AP operations outdoors. Standard Power may also be used indoors as long as all requirements are met. Power is limited to a maximum of 36 dB Effective Isotropic Radiated Power (EIRP), and APs must be coordinated through an Automatic Frequency Coordination (AFC) service. Standard Power is also the only access class limited to operations in U-NII-5 and 7 in the U.S, and as a result gets a total of 850 MHz access.

[…]

> Interference with these users must be strictly avoided. U-NII-6 and 8 are used for mobile operators and would be difficult to coordinate through an AFC. The equipment used is also very sensitive; satellites are a long way away, and the Received Signal Strength Indicator (RSSI) is not nearly as robust as a local Wi-Fi signal would be. Restricting Standard Power access to the U-NII–6 and 8 bands avoids any chance that there will be a problem.

* https://www.cisco.com/c/en/us/solutions/collateral/enterpris...

Power details:

> Standard power can operate only in a subset of the 6 GHz band (the UNII5 and UNII7 bands). Standard power operates most like the existing FCC rules for 5-GHz spectrum. Effective Isotropic Radiated Power (EIRP) is the amount of power transmitted by the antenna of a device. The maximum EIRP possible is 36 dBm for either band (6 GHz adds a maximum power spectral density [PSD] of 23 dBm/MHz, which limits power for narrower band applications). However, to use these higher power levels in the 6 GHz band (UNII5 and UNII7), there must be governance to protect incumbents, as previously discussed.

[…]

> The defining condition of the low power mode is a constant PSD of 5 dBm/MHz. The maximum power level for a chosen bandwidth can then be calculated as 5(dBm/MHz) + 10log(B(MHz)). This means that allowed EIRP will range from 18 to 27 dBm based on the amount of bandwidth used (20 MHz to 160 MHz). When using the higher bandwidth, this allowed transmitted power is very similar to the actual maximum transmitted power in the 5-GHz spectrum.

* https://www.cisco.com/c/en/us/products/collateral/wireless/c...

Some handy charts with frequencies and channels at:

* https://www.linkedin.com/pulse/updated-unlicensed-spectrum-c...

A good presentation by David Coleman from the Wireless LAN Professionals Prague 2022 conference, "Wi-Fi 6E, Wi-Fi 7 and beyond - All about the spectrum":

* https://www.youtube.com/watch?v=HbpD4BRdNvI

From their Phoenix 2023 conference, "Wi-Fi 6E Update: Standard Power & AFC" about how loudly things can be broadcast in various situations:

* https://www.youtube.com/watch?v=F7oovRprO40

The new FCC rules talks about "very low power (VLP) operations in the U-NII-5 and U-NII-7 portions of the 6 GHz band": it's about being mindful of introducing more 'noise' in the spectrum, specifically "power levels up to -5 dBm/MHz could occur anywhere, indoors or outdoors, without any need for a frequency coordination system."

* https://docs.fcc.gov/public/attachments/DOC-397285A1.pdf