I know of no other app which does what they do. Other apps do things like cmd-space (spotlight, which I use ALL the time), ctrl-space (which I have mapped instead of ctrl-b in tmux), shift-shift, which opens search in JetBrains IDEs, etc. Notion could have made cmd or ctrl-/ open that menu at the current cursor location. Adding that one modifier requirement would eliminate so much badness.

As it is now, if your /-whatever is at the end of a line, you're stuck with that popup (hit ESC or mouseclick elsewhere). They even act on the / key within an inline ` code block! So if you want to type a code sample, and you happen to use / toward the end and then hit return as you naturally would, you will in fact select any match in that popup. Who edits code and manually applies styles to auto-syntax-highlighted code?

You may like the slash feature, but I believe strongly that UX educated people would consider this user-hostile. At minimum it is a visual disruption. You can type right on past it and it may eventually go away, but as a user you have to learn to ignore it. It is also absolutely consuming resources while it is going search filtering on every keypress you make until it gives up and goes away. If all you do is use Notion, then it may not be noticeable. But if you are a dev with multiple projects open, multiple local servers running, and other load, you do not need apps that simply waste resources.