You're correct that Google & Mozilla & Microsoft are lying about this.
"We also tested to see if it respects an opt-out mechanism for people who
do not want their home router's data getting scooped up in a broad data
collection: appending "_nomap" to the network's SSID. We combined this with
Microsoft's now defunct opt-out mechanism (for an alternative purpose) of
appending "_optout" to the SSID. We tested each individually and both
orderings of the two by inserting fake scan results, and found that Huq
collected them all."
https://blog.appcensus.io/2021/10/25/what-the-huq/
Mozilla apparently lied when they said they respect the SSID_optout also.
https://location.services.mozilla.com/optout
"Mozilla's client applications do not collect information about WiFi access
points whose SSID is hidden or ends with the string _nomap."
But they lied. See above.
Microsoft is supposed to have stopped using the _optout_ designation.
https://krebsonsecurity.com/2016/05/microsoft-disables-wi-fi-sense-on-windows-10/
"Microsoft has disabled its controversial Wi-Fi Sense feature, a component
embedded in Windows 10 devices that shares access to WiFi networks to which
you connect with any contacts you may have listed in Outlook and Skype -
and, with an opt-in - your Facebook friends."
But they lied also. See above.
They all lied.
https://shirlleycoyle.wordpress.com/2021/10/25/location-data-firm-got-gps-data-from-apps-even-when-people-opted-out/
You can add the SSID_optout_nomap but they won't respect it.
They never had any intent to respect it.
The only thing you can do is not broadcast your home router's AP SSID.
Then the phones won't upload it unless they're set up specifically in the
promiscuious mode which isn't the default except for WiGle or Netstumbler.