@Joelson I can confirm. Setting gpu to off in video prefs makes the composite envelope on the adjustment track mostly ineffective. It seems to only have a small affect on brightness after doing that. Similar affect on Track Fade to Color envelope.
Both envelopes still work normally on regular video tracks with clips on them with gpu off. But I should point out that on regular empty video tracks with the Composite Fx moved to the head of the fx chain, the fx on the empty track propagates to lower tracks (like an adjustment track) but the Composite Level envelope does not control the fx levels with gpu on or off.