Like most European countries there are not so many cycling paths in Portugal. Fortunately the roads are either very quiet or have a wide shoulder to cycle on. In general motorists drive responsibly and give much room to cyclists. Most roads are paved with good quality asphalt except roads through villages which are often paved with the cobble stones which are less comfortable to cycle on.
If you think you can simply follow the official EuroVelo 1 (Atlantic roast route) through Portugal, think again. This route is not marked anywhere. To be precise during the whole trip I only saw a single EV1 marker close to Lissabon.
The suspension bridge across the Tagus in Lissabon is not for cyclists but you can take the ferry from here to Trafaria and then cycle to Setubal.
Further to the South there are some very nice cycle paths between Coimbrao and Nazare. On such such paths I can cycle at a constant speed of about 27 km/h and cover large distances on a single battery charge.
(the area was burned by forests fires in 2017)
Wooden cyclypath with a nice view (somewher in the region of Porto)
The coastline below Lissabon was most attractive with nature reserves and nice beaches. The image below was taken close to Porto Covo where there are many small sandy beaches. It was already end of October and people were still swimming sun bathing there.