A technical challenge on automatic switching

Here is an interesting one and I am unsure if there is an easy way around it....

I have...

A Hub 3 running an M100 connection
Tenda Nova MW6 Mesh wifi
An iPhone X with 30gb of tethering per month
An awful number of dropouts that repeated engineers can't seem to get to the bottom of

I would like to be able to have something that would automatically sense that my connection has gone south yet again and temporarily switch to 4g (without me having to constantly log all my devices into a new wifi network) and then, when the connection comes back, automatically switch back over. Is this possible and what kind of magic router would I need for this to happen ?

Bonus question for 10 points: It would be massively useful if, rather than fannying around getting another sim card and 4g dongle, I could just have my network leech the wifi hotspot on my phone when the cable connection drops and then drop it when the connection returns.....but not sure if this would be possible ? Again, does a router exist that could do this ?

Thanks,

Bill

Plenty of Ethernet routers that have dual WAN interfaces with failover, and lots more that will failover over to 4G connection via a USB dongle

The 4G failover is common in the Asus routers and TP-link kit.

Some Draytek routers have whats called WAN wifi
https://www.draytek.co.uk/information/our-technology...
This I believe will allow what you ask with your phone.

I havent looked at it anymore than that, havent tested or tried it ever so can comment if it actually works.