Looking for suggestions for a nice route from Valencia to Lisboa in 2 traveldays.

Suppose you mean VLC as the big (3d or 4th) city on east-coast ESpana? As there are more as 1.

In fact the choice is extremely limited and there is NO way you can do it without ANY REServ-this is RENFE in ESpana after all.

Day 2 you have to use for the cumbersome MAD to LIS, via Badajoz-Entroncamento, with trains 1 and 3 mandatory REServ.-in between its a tiny dieselcar without-last report said it was full to overcrowded with refugees from UKRayna-they can travel for free. But that may be temporary or just for a day or 2. You canNOT REServe for PT in ES-or reverse.

So you must use day 1 to reach MAD-and there are near hourly AVE superfast trains-most without any stop in between. IF they had (or on the now defunct old line-the middle part is now bustituted) these were just tiny spanish villages without any interest. These take just 2 hrs or so-so you could use a pass to full extent by doing a sidetrip, f.e. to Toledo-but again thats mandatory REServacion on Alvia trenes-a normal busticket migt even be cheaper or cost as much-these also go much more often there.

The centre of ESpana is mostly a fairly dull dry near desert-like area without much interest with a very few smaller towns here&there.

As from VLC there are as of now no direct AVE to Andalucia, this means that the more challenging/rewarding route via there-landing into south of PT=Algarve, then going north is not really feasible. But for this you would need to pay for a busride+ferry in between-beside the unavoidable REServaciones in ES.