[FP3] Fairphone 3 incredibly laggy when unplugged (/e/OS)

After installing /e/OS on my Fairphone 3 I noticed that it is very laggy when unplugged. Choosing High Performance in the Battery settings only drains the battery more and only helps until the next reboot.

After a few minutes of research I found a similar forum post that said that the latest update fixed it. However this was back in the “Android 9 days” and the issue is there (again?).

Any help or fixes?