Every Bitcoin transaction is an inscription. The message and the value are inseparable expressions of conserved energy. What’s being transacted is permanence in time.
Discussion
There's no difference between a bitcoin tx and an inscription data only, without a monetary tx?
Both are monetary. Every bit written to the chain is paid for in satoshis (and energy) through the fee. There is no non-monetary transaction when blockspace itself has a price.
AFAIK both pay the fee, but one carry data, an image or whatever and the other contains only sats as a pure monetary transaction. Correct?
Correct. Both pay the same fee to occupy scarce blockspace. The only difference is what they carry: one moves money as data, the other commits data as money. Economically and thermodynamically, they’re identical.