I don't know how much Flickr is used these days, but I remember it was quite popular some 15 years ago. I decided to search around, and discovered that it is a treasure trove of photos from the period 2005 - 2015, and incredibly easy to search / filter.
Internet archeology is something I've always found fascinating, and I don't think people realize how much data has been lost after we moved to the modern "big tech" internet of today. So many data hosting services disappear back in the mid/late 00s, and with that, the data too. After social media exploded, many just stared storing all their photos there.
It still has plenty of active users (myself included) but it feels much smaller than the 2010s. The groups are great if you can find ones that match your taste, and it’s way more fun to do that and share you photos with human-curated communities than with the algorithmic feed.