The NCBI Assembly database is the most comprehensive source for all types of genomes (bacterial, viral, and eukaryotic).
NCBI offers multiple ways to retrieve FASTA data depending on your needs: Best way to download an entire genome? : r/bioinformatics download genome fasta file
A collection of pre-packaged reference genomes from various sources (NCBI, Ensembl, UCSC) specifically formatted for common bioinformatics pipelines. How to Download from NCBI (Step-by-Step) The NCBI Assembly database is the most comprehensive