It's a fairly minor issue, nothing urgent. But it is a bit annoying and I'd like to fix it if possible

That might prove to be a big "if".

I have KDEConnect on my phone and PC. I also have the client app for Telegram on my phone, and while I'm working on my PC I usually leave the Telegram web client open in Firefox. If someone messages me on Telegram then I get a push notification via Firefox, and a notification on my phone, which results in a second push notification for the same message via KDEConnect. (There isn't anything particularly special about Telegram here. The behavior is similar for other messengers and services that produce synchronized notifications.)

I'll note that this is distinct from the similar issue people have had where their SMS app would produce a notification via KDEConnect's app notification plugin and its telephony plugin. There have been a few threads about that, but I couldn't find anything about this.

I know I can disable these notifications from a particular app/site either in KDEConnect or Firefox, but I'm not always using both at the same time. I'd certainly rather just have two notifications than risk missing something or worse tediously enabling and disabling a bunch of settings every time I use my computer.

A better solution in my mind might be a patch or plugin to KDEConnect's desktop integration. If I have a client open that corresponds to an app then notifications from that app are given lower priority. But this would require my code to know what websites and programs a user has open on their desktop, which sounds like a privacy hazard. I imagine that implementing it would most likely also require a browser extension and some kind of daemon, which sounds like way too much fuss for this silly little issue.

I'd be interested to hear what other people's thoughts are about this -- particularly if you know more about the technical side of KDEConnect.