I mean on the surface, they were both (https://charmed.fandom.com/wiki/Buffy_the_Vampire_Slayer#:~:text=Charmed%20and%20Buffy%20have%20many,to%20hunt%20and%20destroy%20demons.) the big resident supernatural (https://www.dailydot.com/upstream/wb-cw-buffy-supernatural-beginners-guide/) shows (https://buffy-boards.com/threads/charmed-recycling-buffy-storylines.49403/) with female (https://buffy-boards.com/threads/charmed-ones-in-btvs-universe.74217/) leads (https://buffy-boards.com/threads/charmed-buffy-character-similarities-spoilers.6148/) going on The WB (https://buffy-boards.com/threads/would-you-have-liked-it-if-there-were-crossovers-with-charmed-in-the-buffyverse.62882/). There have been Fan Fiction (https://thecharmedcafe.proboards.com/thread/10672/charmed-buffy-crossover-episode) stories (https://thecharmedcafe.proboards.com/thread/5574/charmed-buffy-crossover-century) written (https://www.fanfiction.net/Buffy-The-Vampire-Slayer-and-Charmed-Crossovers/13/95/) online (http://offline.buffy.de/outlink_en.php?module=/webserver/offline/angel.fcpages.com/charmed.html).

gUIgIjrZxEE

In fairness, they were made by different studios, so that right there would've been a major deal-breaker (https://boards.straightdope.com/t/why-was-there-never-an-angel-charmed-crossover/285633). Buffy (https://web.archive.org/web/20061031125231/http://www.jumptheshark.com/b/buffy.htm) was made by 20th Century Fox (so it's pretty much by default, a Disney property now) while Charmed (https://web.archive.org/web/20061031125247/http://www.jumptheshark.com/c/charmed.htm) was made by Spelling Television and by extension, which I assume is now Paramount-CBS by extension.