Probably timing and amount analysis
Pretty trivial for anyone monitoring the chain if they see for example 1.52334 BTC move once then shortly after another address moves the exact same amount minus fees. High likelihood it's the same user. There was a recent example of this with a Zcash whale moving from transparent address to shielded and back.
You can use Monero to break links, but it takes a bit more consideration than a simple swap back and forth (break into different amounts on the swap back, swap at different times, different IP addresses or Tor, etc)
https://x.com/emmettgallic/status/2007137382337040835