Is OP_RETURN dangerous for Bitcoin? Please explain something about OP_RETURN to me?
https://bitcointalk.org/index.php?topic=1166928.0

I saw a discussion that the contents of OP_RETURN can open the value of access to the private key. I am not good at client scripting language. But I assume this is something related to the values of RawTX (R, S) where, when summing the additional value, you can calculate the value of X (that is, the private key). Am I right or wrong?
The method described in the post has nothing to to with OP_RETURN, but is concerned with the SIGOP limits in a block.

Each block has a limit on the number of SIGOPs that can be present in transactions in that block. Signature validation is a CPU intensive operation, and the limit exists to ensure that no block gets too big to validate on regular hardware.

The post describes how a single transaction can be made to consume up to 225 SIGOPS fairly trivially, limiting the number of such transactions in a block to 88. These utxos can be redeemed to any regular output, or an OP_RETURN.

Note that the post is from 2015, and the activation of segwit has increased the total SIGOPs allowed by a factor of 4, so this attack could cost more now.