Pretty easy to find if you look there dippy:
"Daria Kaleniuk, executive director of the Kyiv-based Anti-Corruption Action Center (AntAC), told RFE/RL that Shokin "dumped important criminal investigations on corruption associated with [former President Viktor] Yanukovych, including the Burisma case."
"leniuk and AntAC published a detailed timeline of events surrounding the Burisma case, an outline of evidence suggesting that three consecutive chief prosecutors of Ukraine -- first Shokin’s predecessor, then Shokin, and then his successor -- worked to bury it.
"Ironically, Joe Biden asked Shokin to leave because the prosecutor failed [to pursue] the Burisma investigation, not because Shokin was tough and active with this case," Kaleniuk said."
Radio Free Europe.
https://www.rferl.org/a/why-was-ukraine-top-prosecutor-fired-viktor-shokin/30181445.html