Some nuance is important here.
The world's leading online dictionary: English definitions, synonyms, word origins, example sentences, word games, and more. A trusted authority for 25+ years!
www.lexico.com
PowerPC Macs are
technically obsolete because whilst they obviously continue to be used and cherished by us, they're no longer produced by Apple and they're out of date in many areas when compared to their Intel successors. However, despite what the intermittent trolls who visit this forum would have us believe, they are certainly not
useless because, to paraphrase your own words, no computer is useless if it continues to fulfil the tasks that you require of it.