User interface and player performance in "expert" or "fast" mode on Mac

My config:

Imac 27 "5K 2017 - 4,2Ghz Core I7 4 cores

64 GB of RAM and

Radeon 580 8 GB graphics card.
Prem.Elements 2021 that I just installed is very slow. The video files are HD720 5Mbits / s (very small) and do not play smoothly. While I have no problem with them in Premiere Pro CC 2021 or Final Cut 10.5 installed on this same computer. I recently edited 360 ° videos on this machine in 6K without any worries (on FCPX).
The user interface is very slow (Zoom of the monitor, of the timeline, manual movement of the playhead ...). My projects are adjusted identically to the characteristics of my source videos.

I uninstalled the software with the utility provided by Adobe, installed again ...

Dumped the PRAM from my Mac (CMD + Option + P + R).

Increased the Premiere Elements cache from 2 to 10GB ...

I emptied the Premiere Elements cache ...

I don't know what else to do 😞