I have heard back from our Datacentre SE. The release notes are correct and Cisco has no plans to introduce 1G support on the N9K-C93108TC-FX3 ports Eth1/49-54 via the QSA. So if you have for example a 1Gbit carrier fibre, then it's best to purchase a N9K-C93108TC-FX3P model instead.
Note: N9K-C93108TC-FX3 does not support 1G on QSA/QSA28 adaptor