I'm having a hard time understanding the replies you give about the Hungarian rom.
You want to change the rom?
Also about the custom rom situation, in my experience the best rom I've used when it comes to stability and battery life was the Xiaomi eu ones based on global stable releases.
Other nice mentions are the lineage os based ones that are more powerful but less stable and there is no thermal control that limit the procesor from overheating. Xiaomi based roms have build in thermal restrictions in wich once the OS feels that the phone runs hotter it throttles the cpu down resulting in slight better battery life
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