Speaking anecdotally, this doesn't really ring true for me. I see lots of pro-Palestinian content on Facebook and Instagram, ranging from the sincere to clear disinformation/propaganda. I have friends who post frequently in support of Palestine with zero repercussions.
Attempting to reconcile that with HRW's article: on the one hand I think HRW might be unrealistic about what FB should be expected to tolerate (for instance, they criticize FB for taking down posts praising designated terrorist organizations); on the other, Meta's approach to content moderation - which combines automated systems with overworked and underpaid humans exposed non-stop to awful content - is notoriously fickle and subject to abuse (including, perhaps, by state actors).
Beyond Israel/Palestine, I regularly encounter content on Facebook that the Powers That Be would censor if "the pro-Western censorship regime on FB [were] extremely strong". I think I subscribe to only one political (left-leaning) group (along with a bunch of local and meme pages), but nevertheless my feed is full of tankies demanding we bring back the guillotine and install full communism.