I have had similar problems, but (at least for me) the problem is not with specific dialects or specific accents but with suppressed and blended syllables in natural speech. In my lessons and in most learning material I have used, the speakers tend to speak more slowly and clearly than native Portuguese speakers do in practice.
I remember being totally lost when my MIL would ask something like “Comexdeesh?” (Como é que se diz?) or “Comexdeezest?” (Como é que se disseste?). I spent ages trying to break down the sounds into something comprehensible before I finally just asked my husband. I tried to replicate what I thought I heard a few times before my husband could finally translate the sounds I was making into something meaningful. It is definitely a frustrating experience!
Some native speakers have excellent enunciation or make an extra effort to enunciate when speaking with a learner, but most native speakers suppress letters or syllables and blend syllables and words when speaking normally. Some letter combinations get so smushed together and distorted that they sound totally different from what you’d expect – or even how a native speaker would say them when speaking slowly and with proper enunciation.
The YouTube channel “The Sounds of Portuguese” (link here) uses really nice subtitles that help you follow along and identify the suppressed letters and blended syllables/words. She has one video that teaches you to blend words like a native, but she usually includes subtitles that explain the written v pronunced words in her other videos. She does have an Algarve accent, but it’s still helpful for understanding standard Portuguese pronunciation.
The channel “Listen and Learn Portuguese with Maria” also have a few similar videos on European Portuguese pronunciation that focus on learning how to understand connected speech and blended letters. Here is an example. I think she uses more of a Lisbon accent. (Someone can correct me if I am wrong. I say that because she uses a ‘z’ sound to connect a letter s followed by the letter a, which I think is a Lisbon thing. Some regions north of Lisbon use a ‘j’ sound as a connector in that case.)
I think the Practice Portuguese teams have also made some content on connected speech and blended letters, but I can’t seem to find an example that is specifically dedicated to this topic. Here is a video where they listen to user recording and give feedback. They talk a bit about connectors in that video.
I hope this is helpful! Good luck with your studies 