Back a short ten years ago, Win11 would have been considered malware... sigh - now it is SOP.
Anyway, one thing to remember about S3D is that it is a LOT like SH3, 4 or 5, in that it expects to be the exclusive user of the computer, ~AND~ it also requires the same files, plus more, that Silent Hunter needs, including the DirectX v9.0c library files and a good install of netFramework v2, which is in a netFramework v3.5 install. None of those files are in Win11. So make certain you have all of those in there (Add Windows Features). Skwasjer's first post of the
[REL] S3D - Silent 3ditor thread has his ReadMe repeated, so be sure you review that again. It might be that you have to back out of the netFramework install you have, and then re-install it. Something might be borked there. Also, be sure you are right-clicking on the S3D install msi file and "Run as administrator".
btw, there is nothing wrong (at least, I hope not) with keeping old computers. I still have my C-64 and I do have fun on it about once a month. Similarly with an old something-or-other (Athlon??) dual-boot with DOS and Win98, and I play my SH1, DC, Fighting Steel, etc. on that... then I have an XP / Win7 dual-boot that I use for "professional" audio, since my "professional" multi-track sound card set-up is considered "Legacy" by Windows, and is difficult to get running properly even on Win7... Then I have Win10 here, and a Win11 laptop that almost got thrown on the front lawn - again (the "almost' part lol) - just yesterday...
- The laptop is the only machine I have that "qualifies" for Win11...