I have a 15 inch Macbook Pro 2013 (this one) that I’ve been running Fedora on since F35 using Intel integrated graphics (Nvidia GPU disabled). I noticed a few months ago that kernels newer than 6.8 had worse performance. Upgrading from F39 to F40 didn’t improve performance. I’ve tested kernel version 6.8, 6.9, 6.10 and 6.11.
The performance degradation manifests as a general sluggishness across all applications: Firefox, KeepassXC, youtube is unwatchable due to dropped frames. I can’t see anything that is using excessive CPU or IO.
Are you sure the issue is due to the kernel upgrade? That is, could you replicate it on F39: performance issues with kernel 6.8+ but none with kernel 6.7?
Is there a reason for not using the Nvidia GPU? The 470.xx driver matching that legacy GPU is still available from RPM Fusion.
There were some changes in GTK graphics renderers introduced with GNOME46 (shipped with F40 and GNOME) and then again on GNOME47 (shipped with F41), but those were rather affecting GTK4 apps. See this for a possible fix.