As you may know there have been a variety of background for mass shooters.

A woman shot up google headquarters when youtube demonetized her videos:
https://www.theguardian.com/technology/2018/apr/04/nasim-najafi-aghdam-youtube-shooting-demonetisation-payments-father

A trans person shot up their school:
https://www.reuters.com/article/us-colorado-shooting/transgender-teen-sentenced-to-life-in-prison-for-deadly-colorado-school-shooting-idUSKCN24Q00D

And there's so many mass shootings in gangland in chicago you can't even list them all out.

But the press likes to push only the ones that meet their man-hating narrative - when the shooter is a white man - like recently:
https://archive.ph/hSkPM

Apparently this is his reddit post history:
https://web.archive.org/web/20210813174435/https://old.reddit.com/user/Jake3572

**Of the last 24 posts he made - 12 of them were to one of reddits protected man-bashing hate subs - **IncelsInAction.

The sub description of itself:

This sub is for mocking the antics of anyone who identifies themselves as "incel." This is a term popularised on Reddit and 4chan meaning "involuntarily celibate" i.e. men who can't get laid. Some of them get really really mad about it, and here are their stories...
...
Incels who comment in here can expect to be relentlessly mocked by this community. If you don't like it, don't post here.

Did reddit's protection of it's anti-male subs contribute to this shooting?

It seems a lot more plausible than the banned "men going their own way" sub.