Why on earth go to a 3rd party for information- use the actual train operator.
This is the timetable- currently and for the foreseeable future there is modernisation work on the line and there is a part closure with bus substitution- https://www.cp.pt/StaticFiles/timetables/lisbon-figueira-foz-oeste-regional-trains.pdf
Likewise buy your tickets from the actual train operator- not some 3rd party who brings no benefits to the matter. These are regional trains where you buy your tickets either on the day, or a day or two beforehand- with no assigned seating and which cannot get full.
These are trains that ordinary Portugese use to go about their daily life. People there do not book months ahead, nor do CP open bookings months ahead. Trains which people buy tickets for on the day.
Currently if just going to Figueiro da Foz you would go up the main line and change at Coimbra B to arrive from the north- https://www.cp.pt/StaticFiles/timetables/coimbra-urban-regional-trains.pdf
(there are even slower regional trains on the Lisbon to Coimbra B lines and from Coimbra B to Porto)- So from Lisbon to Porto you can travel on the Alfa Pendular train, on InterCity or on non reserveable regional trains.