I have a Philips OLED804, and the only major problem I have with it is that any surround sound coming from it going to the AV Receiver (through ARC) has a noticeable delay. Anything, from consoles to apps have that delay. If I plug directly on the AV receiver, there is no delay. I tried pretty much any settings combination on the TV and on the receiver, I tried outputting sound to optical, but it's the same. The audio is always delayed... What do?
Go to All settings->Sound->Advanced, enable Digital out delay and set Digital out offset accordingly.
I had the same issue with different model playing video from USB flash. Well I could work with it only by playing using VLC, but at some point after update it was fixed. For newest updates I check this site: https://toengel.net/philipsblog/firmware-download/ because sometimes I see an update here faster than in my TV.
But yea, Philips should work on this, because using default tools you can only increase delay.
The TV should have an option to fine tune the audio delay, if you already played with that then it's clearly a firmware issue.