But Spotlight file search is completely broken, rebuilding the index doesn't help, and web results are the only thing it returns. After 20 years of intense research, Apple finally caught up to Microsoft in race to make search broken and useless.
Aside from that, the Settings menu memory leak (or whatever it the problem is) is very much more apparent on the older mac than it is on the new one, but it's still reproducible. Neither computer is running Tahoe yet, these issues were already present, but based on on your comment, they might now be functionally worse in addition to being a performance and user experience joke.
My new Mac is still amazing hardware-wise, and since those issues seem to just be compensated for, perhaps by having efficiency cores that they're able to delegate background processes to, but the sluggishness and in-adequacy of frontline processes and apps must be embarrassing for what I presume to be smarter engineers than myself who probably just don't get to allocate time or energy toward any of the problems, especially with things like Xcode and SwiftUI also having major issues, and the mac being a relatively small market.
Go into preferences, spotlight and you can add folders to exclude from indexing. I add my home directory and most of the system directories and that more or less fixes the issue.
The last good file search I've ever used was in windows 98. There was no indexing. When you did a search, it looked through all the subdirectories for a filename which matched the search term. It was glorious.
I had the same issue; killing Spotlight processes fixed it. (A reboot would probably do the job too.)
(Killing the process, ofc)
Doesn't seem to be updated for Tahoe yet, and even the Sequoia version isn't notarized, so it's not really clear if it has a future.