Turbo boost on a Dell 7320 no more working

Hello everyone, this is Eddevan from Belgium.

I have a Dell 7320 (not detachable) with an I7-1185G7 processor @ 3 GHz that can boost up to 4.8 GHz in Turbo Mode, running Windows 11. I bought it secondhand a year ago.
It’s actually the Turbo Mode that’s causing the problem.
At first, Turbo Boost worked great; when I used video editing software (Avidemux), I saw the CPU at 100% utilization and running at 4.8 GHz. But for some time now (after a BIOS update?), the speed hasn’t gone above 3 GHz. 
I should note that in the BIOS, Turbo Boost Technology is set to On, as is Intel Hyper-Threading.
I booted WINPE from a USB drive and ran a benchmark, but I still don’t exceed 3 GHz. So it doesn’t seem to be a Windows-related issue.

The battery is charging while I’m running Avidemux or the benchmarks.

Attached are two screenshots: one showing the Avidemux window re-encoding a video and the Task Manager (Windows 11). The other window is in WINPE and shows the “Open Hardware Monitor” program during a benchmark.

Does anyone have any idea why I’m capped at 3 GHz? Since I re-encode a lot of videos, it takes twice as long because the CPU is running slower.
Thanks in advance