Patent infringement threat(Skyhook Holdings, Inc), lack of further investment seems to have been the reason of killing the service around 2021. It seems google location service seems to be the only player in town(other than OpenCellID, which I do not have experience with).
Years ago, there was a UnifiedNLP back-end for Android that used Apple’s service: https://github.com/microg/AppleWifiNlpBackend
Back then it worked fine. No idea about today. That repo isn’t maintained any longer.