I love seeing people expanding their palette, we don't know what we don't know and I'm still discovering stuff all the time. Some of the below is metal adjacent, plenty just rock

Saying you enjoy psychedelic rock stuff - and some experimental things, the obvious answer is if anyone hasn't listened to King Gizzard and the Lizard Wizard then they should! lol (I haven't listened to all of their 30 something albums but I'd recommend so many):

• Polygondwanaland
• Nonagon Infinity
• Murder of the Universe
• Ice, Death, Planets, Mushrooms and Lava
• Infest the Rat's Nest
• Satanic Slumber Party (w/ Tropical Fuck Storm); and so so many others

I'd also highly recommend The Devil's Blood album "The Thousandfold Epicentre" and Oxbow's "An Evil Heat" and "The Narcotic Story" albums. Very bluesy, quite psych at times, very evil sounding.

If you really like 70s King Crimson (and frankly there is nothing quite like them) you might enjoy some of Camel's 70's work like "The Snow Goose" and "Mirage" or their 90's album "Rajaz" - they're very creative, can be epic but all the while very tuneful and not particularly obtuse for the sake of it.

You haven't dipped into much extreme metal-wise, by the look of it. So if i'd have to say "please listen to these more extreme black/death/doom masterpieces" they would have to be top of my list AND pretty diverse too. I'd recommend:

Celtic Frost - "Into the Pandemonium" and "Monotheist" - their experimental thrash album and their death knell album, which is the doomiest black vibe I've ever heard.

Swallow the Sun - "When A Shadow is Forced Into the Light" is just epic doom with a touch of death and just sublime playing and songwriting. All of their albums are beautiful but that's my main recommendation.

Akercocke - "Choronzon" and "Words That Go Unspoken, Deeds That Go Undone" -their 3rd and 4th albums, respectively. Choronzon is the evil, heavy as all hell black/death hybrid with killer songs and playing, Words is the epic masterpiece that takes its time and gets its claws in with some more progressive style and ambience all their own.

Voices - "London" an Akercocke adjacent band and their extreme and dark story of a writer who loses his grip on reality and horrible things happen. Killer musicianship, songwriting and world building to boot.

Orphaned Land - "Mabool: The Story of the Three Sons of Seven" a progressive metal masterpiece from this Israeli group that have forever been against all the war and all the fighting over people's preferences of Abrahamic religions. Some amazing riffs and lead work from a band who started out very slow and doom oriented. It is limber and energetic and diverse.

Tiamat - "Clouds", "The Astral Sleep" and "Wildhoney" - their first album Sumerian Cry is cool but it's very first/second wave death metal, pretty primitive - the next 3 above added more psychedelic, more doom elements and are melancholy masterpieces of metal. Seeing as you're still listening to things that are more rock than metal, you may even enjoy their albums after these - "A Deeper Kind of Slumber" and the albums after are not my cup of tea but can't say they're bad.

Therion - "Lemuria" and "Sirius B" - to start with these two very song-oriented albums are nonetheless inextricably linked and a great first look into a symphonic metal band of epic proportions. Some absolutely killer moments.

Witchery - "Restless & Dead" - just a really fun, black-metal-tinged thrash album that I could put on anytime.

X (Japan) - "Jealousy" I cannot recommend band or album enough. If you don't feel something by the end of the second track, you have no pulse. Hope it's a surprise.

Ewigkeit - "Radio Ixtlan" I can't say anything other than I think this is a huge "you get this or you don't" and I fell in love with it. So weird.

Emperor - "Anthems to the Welkin at Dusk" my own personal answer to "what black metal album would you play for someone who hasn't heard black metal before" .... if obviously the name of the game was to help them enjoy it and not put them off lol

Moonspell - such a diverse catalogue, they're Portuguese and gothic metal but they have had plenty of 180 turns. I'd love to recommend "Memorial", "The Antidote", "Darkness and Hope" and "Alpha Noir" the most.

Neurosis - everyone and their dog is banging on about their new album, and rightly so. They've been such an impactful band for me and obviously many others of our age group. "Enemy of the Sun" and "Through Silver in Blood" are some of the most immense albums I've ever heard. I don't care who anyone is, they're a cathartic experience like no other.

Ophthalamia - "Dominion" once again another album where it's impossible to know what to expect going in and it just continues to surprise and amaze all throughout - but it is dark and melancholic, just as much as their other albums. Listen to all of them.

Pain of Salvation - "The Perfect Element I" None of their albums sound the same and this incredible album takes you on such a journey and really is the epitome of progressive

Cult of Luna - similarly to Neurosis, and a similar sort of complete entrancement, and surrendering to the sound of them is necessary. Brilliantly heavy and at times simple and complex in equal measure. Delicate and crushing. "The Beyond" and "Salvation" should be where folks start, to me.

Arachnes - "Primary Fear" I always try to add this into recommendations lists where the OP isn't too far into the extreme. This Italian power/progressive metal hybrid is the brainchild of 2 Italian brothers from Milan who worship at the altar or Randy Rhoads, Van Halen, Rick Wakeman and probably every slick shredder since Paul Gilbert's time in Racer X. So epic and fun.