IMAX confirms that Denis Villeneuve's Dune 3 is to release in 2026, though there might be a question mark over its Dune: Messiah title...
If you download this PDF report from the Q2 2024 IMAX Investor Presentation, there are charts showing which films are being produced with IMAX in mind all the way through to the end of 2026.
So it looks like Denis is confident with completing the screenplay now, instead of making another film first.