Usually your distro's forums are good enough, and even searching not your distro's forums can lead to some insights into your issues/questions.

Otherwise Arch Wiki, Gentoo Wiki, Arch Forums, Gentoo Forums, Debian User Forums, Ask Ubuntu, Linux Questions, Linux Mint Forums, even Manjaro Forums can be helpful. Always do as much search and research you can before asking your question on a forum and mention what you've done already. A lot of the times, your issue has already been raised and already has an answer. If not, ask away and mention what you've done already.

linuxquestions, arch forums. LQ seems to be a bit less active recently tho

linux mint and ubuntu forum seemed to be very friendly even for noobs

The FOSS websites are usually worthy, as are privacyguides / privacytools, OMGUbuntu, ChrisTitus, and similar. Where are you on your Linux journey? Complete novice, have tried and need specific help or other?

Level1Techs, Lawrence Systems, Learn Linux TV.

Linux Questions was a good forum. I haven't used it in a long time so I don't know if it still is.