That does clear things up. If you search the forum for plywood, you’ll see that with the current laser there are problems with 3mm (it can be done, but carefully) so 4mm is probably a no-go.
The New Module Ideas thread has some discussion of the upgrades, and their rough release date (Q2, Q3). Also see https://forum.snapmaker.com/t/has-anyone-upgraded-their-laser/12074/2?u=edf which covers the limits of the SM laser in plywood pretty well.
My understanding is that the linear module improvements are for precision, and “being quieter” is really more of a side effect. I don’t recall any discussion specifically about making them quieter, but the noise is a common complaint, so I may have missed it. According to https://forum.snapmaker.com/t/when-can-i-preorder-2-5-upgrades/17994/3 they will be on sale in June.
The high-power laser has been discussed for about just as long. Check the Roadmap - should be on there.