You shouldn't worry about what your child says about games or non-electronic toys: these statements are all attempts to see if anything works to get them more of what they want. Saying that nothing else is fun is no different than saying that they weren't paying attention—it's a test to see if it's an excuse that works. You say that he happily plays with non-electronics otherwise, so there is no reason to believe otherwise.
Children of that age are in a phase where they are exploring their own power. They have no idea what their power is, and they want more of what power they discover. Videogames offer, by design, a sense of power via independent agency, which is a form of power that very young children crave and have the least of. The fascination with the videogames is normal at that age, as is the persistent and dramatic attempts to be allowed to enjoy that agency for longer periods. Neither should be cause for concern, especially when you're not enabling habits to form that might cement the seeking behaviour beyond the normal development period of these internal motives for it.
Similarly, the testing behaviour is normal. The child is exploring their social environment to find out what is and isn't possible to get people to do, and at that age they have zero internal concern for any social consequences they cause to others through their exploration.
But! knowing all this is normal doesn't help when you're facing a tantruming child and you're approaching your last nerve. Knowing it's normal is only to help you not worry about it excessively, so that you can save the energy that might be spend on worrying and focus on spending your limited and fraying energy reserves on managing the inappropriate behaviour itself.
Different children respond differently to different structures (aka "discipline" in the overall control and self-control sense of the word, not the punishment sense only), so I can only offer what has worked with my child around videogames and what hasn't, so that you have some ideas to work with.
Things that have not worked to prevent tantrums over videogames:
Asking her to self-regulate time (and punishing lack of self-regulation):
She played as long as she liked, ignoring (at the time) hypothetical consequences of not self-regulating. The actual consequences were too far removed in time from the "offense" to have a meaningful effect on behaviour, which probably felt like a nasty boom-bust cycle of fun and denial.
Having unregulated "fun days" (with the idea that it will "get out of her system" somewhat):
These just resulted in worse behaviour when shifting back to the regular, regulated schedule. She looked for every social means (see "exploration" above) of making the unregulated time the norm.
Pre-emptive warnings that tantrums will result in withdrawal of videogame privileges:
Pre-emptive warnings got ignored until the privilege-removal consequence was already earned, so the warnings had no preventative effect. At this age, their immediate desires are overwhelming compared to verbally-delivered hypotheticals or future events, let alone both.
Things that have worked to prevent tantrums over videogames:
Withdrawing videogame privileges for a day or more when "time up" is met with a tantrum:
Note that this is different from the "didn't work" above, in that it is not pre-emptive warnings, is was simply the implementation of a known and naturally-connected consequence when tantrums happened, with an reminder of why the consequence was happening only given after the fact. Skipping the lecturing about consequences and just implementing them saved my energy and didn't allow her to assign responsibility for caring about consequences to me, which is what was happening when the consequences were primarily a verbal subject. Of course, the immediate tantrum just got worse, but it paid off in reducing and then completely eliminating them later.
The inevitable passage of time and the resulting increases in maturity:
She simply got a bit older. The above point probably helped her internalise the knowledge that a poor response to "time up" resulted in withdrawal of videogame privileges, which not only reduced tantrums, but possibly gave her some practice with self-regulation. She's still only 6, yet notably better at accepting statements that the videogames aren't going anywhere and that there are other things to do. She also now actually self-regulates sometimes, turning it off before I even ask her to; that happened without me attempting to teach the idea of self-regulation verbally.
Again, children are all different. Mine is very "stubborn", in the sense that she is strongly motivated only when she has internalised the reason for doing something, or has independently discovered her own reasons for doing something. Showing rather than telling works very well for her, which can involve implementing consequences with what feels like "too little" warning, but is far more effective than giving her lots of verbal instructions that end up just being good targets for her to practice arguing techniques.
