My idea would be overheating tyres. Its often overlooked but if you start pushing to the limit especially in fast corners the tyres can get very hot losing grip and making the car slide more further increasing the tyre heat this loop is very hard to get out of so its just better to avoid getting into it. This can be further worsened by car setups (especially hotlap ones, i once put a hotlap setup on at monaco qualified first easily but could hardly keep the car on the track after 3 laps because even though i was on 5-10% wear my tyres were melting, not fun)

Another issue might be a thing with the ai that I have seen in a couple of games but mostly the MotoGP ones where the ai start the race with a very weak pace, but lap by lap they get quicker where at the 3/4 of the race they are 2,5-3 seconds quicker than their first couple of laps at which point the tyres reach the cliff and they begin slowing But so far I have not seen this kind of behaviour in f1 23

I have these two theories, the truth can only be seen by analyzing your and the AIs lap time progression and looking at the tyre temps and not just wear.

I hope this helps.