Article below covers many things already discussed earlier in this thread, but is a good summary of EU LTR.
However I suspect that LTR has same fundamental problem as Portuguese PR - the application process has been broken for years.
Following bit from the article helps (somewhat) to explain the differences between EU LTR and PT PR:
Long-Term Resident Status vs. Permanent Residence Permit
Although both legal regimes provide long-term residential stability, they differ significantly in their legal scope.
A Permanent Residence Permit produces legal effects exclusively within Portugal, whereas the Long-Term Resident Status has a European dimension, enabling its holder to benefit from facilitated procedures for establishing residence and pursuing employment or study in other Member States of the European Union.
Furthermore, the financial eligibility requirements are more demanding under the Long-Term Resident Status, requiring applicants to demonstrate the stability and regularity of their financial resources, reflecting the enhanced legal rights and responsibilities associated with this European status.