Taken from the Wiki General Enhancements:
"Note: General enhancements stack, so combining them amplifies their effects!"

This effect doesn't seem to be applied to the mob farms. Tested with a similar setup provided in the wiki.
Using a Nether Fortress Farm Tier 2 yields 26 progress per tick. With one speed enhancement it provides 146 progress per tick.
With two speed enhancements it provides 146 progress per tick and with 3 or 4 it still only provides 146 progress per tick.

Testing with loot enhancements or other enhancements seems to only give the initial effect of one applied and multpile aren't counted.

Tested on 1.20.1 with v8.6.1 and v8.6.3