The bug
The default brewing_fuel component for blaze powder references the cooking/speed_default number provider as its speed_multiplier instead of brewing/speed_default, which goes unused.
This has no visible effects, since cooking/speed_default returns 1 for almost all blocks, including brewing stands.
How to reproduce
Hold a blaze powder item
/execute if items entity @s weapon *[brewing_fuel={speed_multiplier:"brewing/speed_default",uses:"brewing/uses_default"}]
Expected result
Should say “test passed”
Observed result
Says “test failed”
Notes
You can see the default components of items with the data generator reports too.
Can confirm: