In our two bathrooms we have a switch panel with 4 switches: one for a light, 2 for heat lamps, and 1 for a fan extractor.
As we tend to forget the fan extractor I want to make this smart.
Something like 
It has to work well with Home Assistant. WiFi is fine, Zigbee would probably be better. Should not have a cloud dependency, I can't sell this stuff to my SO saying that she can't turn on the lights if the internet is down. I've flashed Tuya based switches and RF emitters with ESPHome using LibreTiny.
As it's obviously 220v I'd like to avoid Aliexpress stuff. Probably also needs a good IP rating as it's in the bathroom.
Any tips?
I use a Shelley 1 for my bathroom fans. Shelley's all over my house for lights, something like 30 of them, very reliable.
All tied into homeassistant for automations. I use a humidity sensor to turn bathroom fan on and off.
So, there's no way to manually turn it on? In my case, I'd add the Shelly inside the well, wired to the Fan, and will always have the Fan switch on?
Yep switch this still works. Can be switched on by switch, automation, or push on phone.
Should say you if you just want a simple timer you can (e.g. turn off street 30 mins) you can do with newer Shelley versions with built in scripting if you don't want to go for full automation system like home assistant.