Inline Barrel Adjusters with Shimano 105 R7020?
If you have the newer FD-5801 you don’t need the dedicated inline barrel adjusters. The derailleur itself has a built-in tension adjustment hex screw. It rotates the cable clamping point around which effectively shortens or lengthens the cable.

See page 18 in the manual: https://si.shimano.com/pdfs/dm/DM-RAFD001-05-ENG.pdf


  Adjust the cable tension with the cable adjustment barrel (C) or cable
  adjuster on the frame so that the bracket indicator (B) or (E) is
  aligned with the input link indicator (A) or (D).


Of course you can still install inline barrel adjusters. They allow for an increased adjustment range, can be adjusted while riding and don’t require a hex key.

The FD-5800 doesn't have the integrated cable tension adjustment.