That's on the pitching side not the hitting side. Baseball-reference derives pitching WAR through runs allowed while fangraphs derives pitching WAR through FIP.
The position player side typically has gaps because baseball-reference weights defense much more heavily than fangraphs does and they use different measurements to evaluate defense. Baseball-reference uses DRS and fangraphs uses OAA/FRV.
For reference this is Caleb Durbin's value by b-ref and fangraphs this year
B-ref - -2 runs batting, +2 runs baserunning, +9 runs fielding, +2 runs positional adjustment which is 11 runs above average plus 12 runs adjusting from average to replacement. That leaves him 23 runs better than replacement for 2.3 bWAR
Fangraphs - -4 runs batting, +1.9 runs baserunning, +3.6 runs fielding, +1.3 runs positionally, they have +1.7 run adjustment to league average then plus 10.4 runs adjusting from average to replacement. That leaves him 14.9 runs better than replacement for 1.5 fWAR.
So Durbin has 0.8 more bWAR than fWAR and defensively baseball reference has him 6.1 runs better than fangaphs does defensively so 75% of the gap between the two comes from defensive value.
This is why Turang had a huge gap between bWAR and fWAR in 2024. DRS viewed him as +22 and FRV viewed him as +5. Bref viewed his defense as worth 27 runs and fangraphs as worth 5.6 runs which is how one ends up with 4.8 bWAR and 2.6 fWAR.