My advice for this type of situation has been a 4G/5G modem-router+directional external antennae.
They are more sensitive so they can work with a weaker signal, and they don't move once installed somewhere, pointed at a cell tower. That means the connection can be made way more stable than when using cellular data on a phone.
Combine that with a prepaid data SIM, and you wont waste any money when you're not there using it.
Roku?