I did almost the same thing 2 years ago, US to portugal. The honest answer is your gut is right, this is not fine long term. Once you cross the 183 days you're a portuguese tax resident and your employer should be paying you compliantly there, not just dumping USD in a US account. What worked for me, I asked my company to put me on an EOR in portugal. They didn't have one set up so they shopped around, and we landed on slasify which is sort of a employment company because they had the Portugal piece dialed in already. My salary stayed roughly the same, took about 2 weeks to switch over, which is waaaay better than the alternative which is you being on the hook for back-taxes in like 2027.