The T95 Allwinner H616 TV box comes with an Allwinner H616 processor that is unique to this device. Some people think the processor is clocked too high by default. And since the processor is constantly clocked at 1.4GHz, they would like to try to reduce this by installing a custom ROM. These TV boxes do indeed come with firmware and will get firmware updates, so it is plausible to think a custom firmware version may exist for it; however, you don’t typically find custom ROMs for TV boxes as you would an Android smartphone. That said, there are files on the internet that have particular firmware updates where the CPU has varying speeds. For instance, Elm44 on XDA Developers has said they have tested firmware version 10.1.X18 and can attest to it having several new features, one of which is more “CPU frequencies.” But unfortunately, the link they shared is no longer working. (If anyone finds another one please leave it in the comments and I will upload it to my own cloud storage so it can be kept.)
XDA senior member Bertonumber1 has the T95 H616 TV Box running on Magisk 20.4 direct install T95 h616-10.01.14. X18. It has “decent” firmware with build.prop tweaks, but they fail to mention if it is the same firmware that has the CPU frequency changes. If I look at the firmware build numbers, though, it would appear as though it likely is the firmware with the CPU frequency changes. According to the same member, you don’t need root access to install the firmware; you just need the Phoenix USB Pro.