About retrieving the sequences of gene familiess

hi. I am trying to retrieve the sequences or/and representative sequences of the uniref90 gene families and species in the samples_genefamilies.tsv output file from humann3. I found that the uniref90 accession names in the files are not in the uniref90 database. I found that these names are constructed in the following way: ‘Uniref90_’ + UniProtKB accession number. Such as these ones: UniRef90_C6JF93; UniRef90_R7PFX; UniRef90_D4LFR6. And many of them are not the accession numbers of the representative sequences of the clusters. I am uncertain what to do now. Should I just ignore the ‘Uniref90_’ part in the name and query the sequences only using the following UniProtKB accession numbers? And can I retrieve the sequences of the specific species within the same family?
Best regard