Unfortunately on machines doing a lot of software development, the various dependency cache locations need to be excluded from indexing, otherwise Spotlight is essentially doing full text search over millions of lines of code
For me newly installed apps from outside the Appstore are excluded from Spotlight until I manually open them and trigger the 3rd party “untrusted” confirmation dialog. After confirming with Open they show up.
MacOS 26 actually has some really great new features around Spotlight, from actions to clipboard history, and the heretofore-underloved Control Center has been really improved (and is clearly being positioned as the new solution to the plague of ever-increasing menu bar icons). There are improvements to Shortcuts automation. And, for nerds (hi), Terminal finally got 24-bit color and support for Powerline fonts.
I see a lot of "ugh, Tahoe is just the iOS-ification of macOS" on HN, which, on the surface, I get -- the visual changes by and large make things worse, and ironically I think they're actually not as good as the changes on iOS. But the Mac got stuff that the iPad didn't, and there's still a lot you can't do on the iPad that you can on the Mac. I don't think the two are merging any time soon, even if they're becoming more visually similar. (Actually, I don't think the two will ever merge, strictly speaking, but that's another post.)
It's possible that happens to me, and I've not noticed it. I don't add new applications that often, so I can't recall the last time if it showed up immediately or not.