ARI Holders (Stage 5)

The rules on staying in Portugal have not changed, although the timings of renewal have changed since 2020. For the rules, which can be very strictly applied, see: The end of Portugal's Golden Visa—for real this time? - #1362 by Onward. To make it one trip 14 days you could have 7 days on the end of your 1st year and 7 days at the beginning of the 2nd year GV, if you want to make it a single trip. Portugal is not exactly a hardship destination. But I wouldnt be tempted to test/push the SEF bureaucracy on this one…
For proofs see: 14-Day Requirements: Proofs.
With online renewals they do not seem to require documentation this year- see: HOW-TO: GV Automatic Online Renewal Procedure (Jan 2023→). But nobody knows whether the online procedure will continue. We live in hope!!

There are several pieces of documentation to exchange a Singaporean driving licence for a Portuguese one (The search function gave me your location) . You will need
Proof of residence (GV)
Medical exam (perfunctory -vision and ease of movement, and this can be done at any Automobile Club de Lisboa) - the doctor fills out the form and sends it to IMT
Numero de utente (health service number)
Valid existing driving licence & certificate of authenticity of licence. The certificate of authenticity can often be obtained online, but Im not familiar with the Singapore situation. See here:Exchange a foreign driving licence for a Portuguese driving licence - and Instituto da Mobilidade e dos Transportes, IP

A caution: Do not believe that you will get the new Portuguese licence within 60 days (as in the FAQs). Plan on the assumption that you will not. If you are in Portugal for more than 2 months, you will get a “Guia” which authorises you to drive in Portugal for the 2 months of the guia. The Guia can be renewed, but the Guia is not valid outside Portugal. I had to apply for a Portuguese licence twice, the first time exchanging an EU Driving licence to Portugal DL. It took almost a year (I spoke to the head of IMT Lisbon & asked for my EU original back so that I could drive in France -which prompted IMT/Lisbon to issue the PT licence promptly). The renewal was done within 90 days not 60 days (so I had to get an international driving licence to cover me for a trip outside, and fly back to obtain the renewal!).