This is an established local convention that works quite well in practice. Please follow it, or discuss it first before making widespread changes to the map.

Avenida Ceres is exceptionally narrow, why was it reclassified from service=alley?

service=alley#Narrow_historic_streets

osm.wiki/Pt:Tag:service%3Dalley

Vandalismo: balsas fictícias.

Vandalismo: balsas fictícias.

Vandalismo: obra de estrada fictícia.

Vandalismo: balsa inexistente.

Não há nem balsas nem atracadouros aí.

Vandalismo. Ponte está em obras de reparo.

A BR-239 entre Itaituba e Humaitá não pode ser troncal porque não é pavimentada. Veja a regra 2.1:

osm.wiki/Brazil/Classifica%C3%A7%C3%A3o_das_rodovias_do_Brasil#Crit%C3%A9rios_da_proposta

Ela de fato é uma exceção conhecida porque, pelas regras que foram votadas e aprovadas nacionalmente, não poderia sequer ser primária. Mas a comunidade decidiu abrir uma exceção nesse caso por causa do contexto local. A exceção ficou registrada aqui:

osm.wiki/Brazil/Casos_especiais_na_classifica%C3%A7%C3%A3o_vi%C3%A1ria

Por favor, observe essas regras e exceções, e se tiver alguma dúvida, entre em contato com a comunidade pelo Telegram, temos um grupo lá dedicado a discutir questões de classificação:

osm.wiki/Pt:Canais_para_contato#Telegram

This is the main route between Marabá and Santarém, both with a population greater than 260 thousand people. 248 km in the middle is unpaved, out of 1065 km total. That means 23% is unpaved. When the local community discussed the implementation of this system in 2020, we agreed that, when the majority of the route is paved, the paved stretches rooted on each side can be classified as trunk. If you have any questions, reach us out through Telegram. One of our groups is dedicated entirely to debate Highway Classification (group "Classificação de Vias"): osm.wiki/Pt:Canais_para_contato#Telegram

That was incorrect too, so I reverted it. The route is fully paved and it is the main route between two cities with more than 200 thousand people: both Marabá and Parauapebas have more than 260 thousand each.

This too is incorrect. This is the main route between Imperatriz and Marabá, both with more than 266 thousand people each. So it must be trunk, not primary. The fact that it goes through smaller cities does not make the rules for primary take precedence. This is clearly stated: "Each way should be assigned the highest classification level that satisfies any of the applicable criteria below." osm.wiki/Brazil/Highway_Classification_in_Brazil

That's incorrect. The route you downgraded from trunk to primary is the main route between Belém and Marabá, both cities with a population greater than 200 thousand. Belém has more than 1 million people, and Marabá has more than 266 thousand.