Election board is not lead by Abiy's party and is fairly independent institution this time that is lead by former opposition leader and well known political activist Birtukan Mideksa. PP got slapped many times by the election board including in Somali region. Abiy's party can't declare victory this time. I personally know some of the people who are leading the election board. They are former journalists, bloggers and political activists who were jailed by TPLF for their stand for democracy. PP will not get away with any vote rigging this time like TPLF.
PP knows that it has zero chance of manipulating the election board so it did a "smart" job of going after some opposition leaders in Oromia and Addis Ababa. PP knows if OFC and OLF were to compete in Oromia, the chances of PP wining will be not big. So by going after their leaders, PP was hopping the radicals in the party will force the party to boycott the election "until our leaders are free". And they did just that. The Addis Ababan based Balderas understood what PP was doing and refused to boycott the election even if their leader are in jail too. But they knew what PP was up to. The Oromo party leaders were a bit emotional and just run into the trap of PP and boycotted it which was exactly what PP wanted.
We have 48 legal parties in Ethiopia and only 2 boycotted the election. Both are Oromo parties OFC and OLF. All the others are participating.