Hello,
Based on what you've described, I do not believe this is a Bose headset issue. The fact that the same Bose QC35 II works correctly under Bazzite/Linux and that the audio starts in sync before gradually drifting out of sync points more toward a Windows Bluetooth stack, Bluetooth driver, or audio pipeline problem than a hardware fault.
The most useful troubleshooting step at this point is to determine whether the issue follows the Bluetooth controller or the Windows installation. Since you've already ordered the TP-Link UB6A, I would test it after completely disabling the Realtek Bluetooth adapter in Device Manager, not merely leaving both adapters installed. If the lag disappears with the alternate Bluetooth chipset, that strongly implicates the Realtek Bluetooth driver stack or its interaction with Windows 11 24H2.
I would also check whether the problem started after the installation of Windows 11 24H2 itself or after a cumulative update. The symptom of audio progressively falling behind video rather than having a fixed delay often indicates timestamp synchronization issues, buffer management problems, or a regression in the Bluetooth audio stack. Since the issue is present across YouTube and local media players, the common denominator is Windows audio over A2DP rather than any specific application.
Another area worth checking is the active codec. The Bose QC35 II primarily uses SBC and AAC depending on the Bluetooth stack. You already tested the BluetoothAacEnable registry setting, but Windows may still be negotiating a different codec path after recent updates. Capturing a Bluetooth ETW trace with Bluetooth and Audio providers enabled would provide definitive evidence, although that is generally more work than most users want to invest.
Given that you've already tested re-pairing, audio enhancements, Hands-Free Telephony, power management, alternate drivers, and registry settings, and considering the issue does not occur under Linux, I would focus almost entirely on either a Windows 11 24H2 regression or the Realtek Bluetooth implementation on the RTL8922AE platform.
If the lag remains when using the TP-Link USB Bluetooth adapter with the onboard Realtek Bluetooth disabled, then the evidence shifts heavily toward a Windows audio stack issue introduced by a recent Windows update. In that case, there is unfortunately little that can be corrected locally beyond testing with a newer cumulative update or waiting for Microsoft and the hardware vendor to address the regression.
I hope you've found something useful here. If it helps you get more insight into the issue, it's appreciated to accept the answer. Should you have more questions, feel free to leave a message. Have a nice day!
Domic Vo.