Want to stay a month in Portugal any recommendations ?

Jan is likely wet and somewhat cold/cool. I was in Portugal for 10 days in Nov 2023 and it was raining more than 50% of the time. Do some research on the outer islands in the Atlantic, such as Azores. Hope the weather is better there.

As the previous poster wrote, January is historically a wet month. Rain for ten days straight is unusual, but can happen. However, for the vast majority of the country the temperatures are well above zero and, usually, we have sunny days along with the rainy ones. I love the sunny winter days and can frequently eat outside even in January.

If you are coming from a very cold, snowy area, it will be a great improvement.

Apart from weather, and a month will easily get filled:

Lisbon (cable cars, if you can get on one; load Rick's city walk)
Monastery of Alcobaca
Sintra (stay over as there are 3 excellent castles/ruins)
Nazare surf museum in the lighthouse (a must)
Obidos (Casa do Relogio!!)
Conimbriga Roman ruins
Coimbra
Quinta de Marrocos on the Duoro River (be willing to spend money for everything they offer; a nice splurge)
Evora (skip the Chapel of Bones)
Escoural Cave near Evora (must arrange a visit)
Algarve!! (and stay in Lagos)
Sagres Navigation School (walk along the cliffs)
There. That should keep you busy. And skip Fatima
Go get 'em! We are headed back ourselves this fall. A wonderful country.

Are you thinking of one location or spending time in multiple locations?

Julie Dawn Fox blog is a good place to look for ideas. She covers some of the smaller towns (that are very much worth visiting) that Rick Steves does not.

Learn some European Portuguese. Simple phrases that are commonly used in a service setting for a start. Don't forget to greet people with "Bom Dia" (or Tarde/ Noit depending on the time of day) when entering shops/restaurants etc.