Last.fm is still used quite a bit, mainly as a listening history tracker rather than a radio or recommendation engine.
Spotify is still the only big streaming service with native platform-level scrobbling. For everything else it's a lot more DIY, usually with third party tools at the device level.
A big reason it’s still relevant is the ecosystem around it. The API hasn't really changed in 15 years, which makes it easy to build tools where a username alone is enough. That kind of lightweight social integration has mostly disappeared elsewhere.
Today, the social / community side is almost entirely just Discord. Nearly every music related server has a bot that displays Last.fm stats. My estimate is that abut 10% of Last.fm their users are also active in Discord music communities.
(Disclaimer: I run .fmbot, a Discord bot that integrates with Last.fm.)