Do you think it's my bad written english that makes people not to reply my cold emails?

Use Grammarly (browser extension) to take that out of the equation.

Cold emails are difficult no matter what - But definitely show us an example if you're worried and we can see if your concerns are valid - many non-native speakers write better than natives, so you could be fine

You can hire freelance proofreaders and editors as well if you want to be extra sure.

Are they always the same mails? Cold emails which don't even address me personally will end up in my spam folder.

For example, I have multiple email addresses and got the same mail ... smth like:

Hi

I am *** from ***

I wrote to you a few days ago to check if you're considering *some stuff*

Since I didn't hear back from you, I'm guessing you were busy and am sending a quick shout out.

To help you decide *some links, stuff and pla*

I'd love to brainstorm on a call if you think it is of value.

I guess a lot of people don't like getting mails from people they don't know. I feel that way about it. It's more pleasant if at least one person has dealt with my stuff / bio / projects and then refers to them.

like:

Hi

I am *** from ***
I saw you working on *name of project*. That's really exciting.

*... and so on *

Please show us an example of what such an e-mail from you looks like. Then we can say more about it. ;-)

Maybe provide an example of an email here?

Tone is often quite difficult to get right in a cold email. Those with perfect written English still don't get it correct. It may even help you to express that your written english is not great, or at least express that you're uncomfortable and see if you can schedule a call to discuss it.
There are 2 other formats you can take advantage of: Send a video using loom.com or send audio notes with audionot.es

Yes.

But also conservatively 70% of people aren’t going to reply to your cold emails anyway.

Cold email can be highly effective but even when everything is perfect conversions are low. Any negative effect compounds. Cold email is all about communication and if your emails give off cues, even subconscious cues, that you/your product might make life more confusing vs less confusing for them they are much less likely to respond.

I get cold emails from scammers and everyone else who does it may as well be the same.