Is it okay to copy and paste content from my blog to other channels?

Google doesn't penalize duplicate content, that's a myth. If you syndicate content on other websites just make sure to use the canonical tag.

For Reddit and other social media I honestly don't know, but if you make sure to let Google index the content on your website first I think you'd be fine.

One thing that we do is share it on Medium.

Whatever goes in our blog horizontech.dev/blogs also goes to https://medium.com/@HorizonTech_dev (need to automate that. Not sure medium provides an api)

Not sure whether it hurts in SEO or not. (We find the medium SEO is better than ours)

As far as I know, you won't get any penalty from Google. But you can get a penalty from communities and platforms, which is worst.

So it depends on how you post.

For me, there are two kinds.

1. Trasher.
2. Insider.

Trashers are not welcome in any community. They don't care about the people, they only care about their self-interest. Here is an example post from a trasher:

Hey guys,

I wrote this about this topic. Blablabla.
Two
More
Paragraphs and link.

The community will be like: Cmon, fuck you and as a result, you'll have no traction to your site. Furthermore, you'll ruin your reputation.

Insider

They regularly interact with the community. They always provide value upfront and then at the end of the post, they could add a handle or link.

https://www.reddit.com/r/Entrepreneur/comments/f87yc6/the_dracula_strategy_generating_b2b_leads_on/

Here, this is one of my posts on Reddit.

Just like in life. You need to give first in order to ask.