There is actually a Chinese solution to this which you wouldn't prefer at all. Legally every place who provide free wifi will need you to do sms verification with your smartphone, and record your ip with your smartphone number (which in China is connected to your identity). Then they need not worry about liability, because if anything goes wrong, they can tell the police exactly who you are.
If you want both privacy and liability, it seems indeed only you can do is to be harsh on larger entities like cafe shops who provide free wifi.
Actually you cannot use your present Mullvad account to do so. Instead, Mullvad provided exclusive API for tailscale as partner account to do so, which you can only get from Tailsacle if you choose their service. Mullvad only allows those data to go through its server.
Given that Tailscale is a ridiculous company that advertises on privacy while force user to login via SSO by tech giants or OIDC which is shit in privacy, I will stick to my current origin Mullvad account and keep away from this service.
It is really fascinating that the first website I went to is exactly named "Why bkuhn's Website Looks Like Crap", where someone explains why he is sticking to Web 1.0.
I haven't use the app you mentioned but KDE connect and a notification log app I use both can do this.
I think maybe you forget that they need to first get the accessibility permit before it can read notification, which is a very high level permission in Android. You cannot even grant it directly in normal permission menu and there will be pop up warnings. (Well then there is the question of how many 0day on earth are there in android)
There was a fascinating (but sadly discontinued) app called Shortcat for MacOS. It basically let you control your entire MacOS with keyboard typing texts.
Thus, this can actually be done at larger scale for over 10 years.
Update: It turns out the development is resumed again, but I don't use mac anymore.
It only detects if there is a block in the browser that does not serve as website rendering. Since I use Tree Tab on side panel of Firefox, this plugin will believe I have opened devtools all the time.
Edit: it will think I closed devtools when I really open devtools. I start to wonder how shitty the code is.
If you want both privacy and liability, it seems indeed only you can do is to be harsh on larger entities like cafe shops who provide free wifi.