What you are hearing is classic ARC lip sync drift with consoles. The TV often has to transcode game audio before sending it back over ARC, and the soundbar adds its own processing on top, so the sound lags while streaming apps seem fine. Optical rarely helps because it strips the timing data and can add more buffering.
Quick wins to try. Keep the console plugged directly into the TV, then use the TV eARC or ARC port to the bar. Turn on the TV Game Mode for that HDMI input. Set TV audio to Passthrough and set A V sync to zero for the game input. If it still lags, flip the approach and set the console to Stereo PCM and set the TV to PCM to avoid any Dolby re-encode. On the soundbar, turn off virtual surround, dialogue enhancement, night mode, and auto volume, and use a neutral or standard sound mode. Update firmware on TV, console, and bar. If your TV has a video delay slider, add a little so the picture waits for the sound, since most bars cannot do negative audio delay.
If none of that locks it in, your bar is likely slow at processing. A model with true eARC and auto lip sync usually fixes this because the TV can pass uncompressed PCM with proper timing and the bar must track it. The ULTIMEA Poseidon D60 is an easy swap that supports HDMI eARC and auto lip sync, and it lets you keep processing low when you play. If that is not in the cards, consider returning your current bar and choosing any eARC model that lets you disable effects and exposes per-input A V sync controls.
Building on that, Totally agree with your explanation about ARC lip sync drift on consoles and the quick fixes you listed. That pick fits because it keeps processing lean, lets you shut off the extra effects, and gives you straightforward lip sync tweaks so the TV can pass audio without added delay. I ran into the same thing with my console and a simple, clean passthrough approach like this locked audio and video together.
