Thanks. Yeah, that’s where my brain was going, why introduce more variables like change in tx or tx order, if you can keep these fixed and just iterate on nonce. But I have no idea how this works, so with every comment I’m learning something new.

Might help you grok this if you mess around with a SHA256 calculator, like

SHA-256 hash calculator | Xorbin

SHA-256 algorithm calculator

Paste in the first paragraph (the description under the calculator, starting with "The SHA") and it'll give you a hash that starts with ae8b. If I told you to make changes to that paragraph until you generate a hash that starts with 0, you should hit that target once every 16 modifications on average, regardless of if you start adding letters to the beginning, subtracting from the middle, or changing punctuation at the end. Instead of that paragraph, hashers are using block templates and nonces as inputs. Both can change every time, or just one can change, and the odds of finding a hash below the target isn't affected by which one is changing (or if it's one or both).