Well, most decisions are outsourced to the board members, who's membership is the main thing shareholders vote on.
Mandatory reporting kicks in at 5 percent ownership. At 10 percent, the SEC considers you an insider[1]. Before that, I doubt board members even know you exist unless you talk to them first (and they aren't taking your calls or mine).
[1]: https://www.sec.gov/smallbusiness/goingpublic/officersanddir...
I don't know what scrutiny that brings, but Warren Buffett has been careful not to get Berkshire Hathaway designated it. I believe the limit is/was 10%, but then you could ask the Federal Reserve for a higher limit, which they did because of Bank of America or Wells Fargo I believe? I don't know a tremendous amount about it, but from what Buffett was describing, it wasn't the fed asking them about their bank holdings, they were asking the bank about them.
https://www.investopedia.com/ask/answers/040315/what-can-sha...