Amazon finally listed the Fujinon XF 400 mm f/4.5 for preorder here
The Fujifilm X-T5 with XF 16- 50 mm f/2.8-4.8 is also discounted by $200 at B&H Photo / Amazon / Adorama leading up to the announcement of the Fujifilm X-T6.
Fujinon XF 400mm f/4.5 R LM OIS WR: B&H Photo / Amazon / Adorama