TapNoiseIf your Mac keeps changing a name or technical term, inspect automatic spelling correction in the app first. You can often keep spelling suggestions while stopping automatic replacements.
Find the app-level control
Look under Edit › Spelling and Grammar for an automatic correction option in supporting apps. Turn it off and type the troublesome word in a new sentence.
A website or editor may implement its own autocorrect. If the behaviour occurs in only one application, investigate that app’s preferences before changing every input source on the Mac.
Review the default
In System Settings › Keyboard › Text Input › Edit, inspect Correct spelling automatically and the spelling language. A mismatched language can make ordinary words look incorrect.
Also check Text Replacements if the same short sequence always expands into a different phrase. That is a deliberate replacement rule, not necessarily a spelling correction.
Keep useful checking
Disabling automatic changes does not mean you must abandon proofreading. Use the app’s spelling command, inspect suggestions and read the finished passage yourself. In code, names and syntax should be reviewed using the editor’s language tools rather than prose correction.
For punctuation changes, use smart quote and dash settings. If the characters are wrong before any correction occurs, check the selected keyboard layout instead.
Source: Apple’s Input Sources settings.