Big Sur available and then Monterey Only the Next. Why?

My mac book pro (2019) was showing up an upgrade to Big Sur a few months ago, when I was unable to upgrade due to company VPN client incompatibility. Now, I want to upgrade and was all prepared, having tested it on spare Big Sur upgraded mac, but now the new MacBook pro (2019 Intel) shows only Monterery. I want big sur first, not Monterey. How do I force Big Sur first?