Is there a way to make selection using a brush?
Hello @Julian_Carlo_Fagotti and welcome back to the forum!
Maybe the plugin Paint selection does what you want?
Michelist
Add/Edit: In the topic of the plugin the original download is no longer available, but you find the new download a few posts lower in that topic, as well as in this topic, because I took the freedom to add it here too. 
Happy downloading, have fun!
Also, you can convert a paint layer into a selection mask with right-click → Convert → Convert to Selection Mask.
That makes a Local Selection mask that you can further paint on in grey.
And you can paint, in grey, on the Global Selection mask that you get after you’ve used a Selection tool.
NĂŁo achei o plugin.
That is no problem, I got it in my cloud, you can download it from here:
By the way:
Este Ă©, por acordo e estipulação nas regras do fĂłrum, um site de lĂngua inglesa e todos os utilizadores sĂŁo explicitamente encorajados, se postarem na sua lĂngua materna, o que Ă© absolutamente correto, a adicionar uma tradução em inglĂŞs Ă s suas mensagens.
Trata-se de uma prática que tem funcionado muito bem no fórum, pois permite obter uma tradução mais exacta de uma tradução eventualmente pouco clara, inexacta ou mal escolhida, com a ajuda do texto original e de outros tradutores.
Isto nĂŁo Ă© nada de invulgar aqui, mas, acima de tudo, facilita a comunicação entre todos nĂłs, de modo a que ninguĂ©m possa traduzir os textos da sua lĂngua materna por falta de conhecimentos linguĂsticos ou informáticos e seja marginalizado.
Afinal, quem escreve aqui na sua lĂngua materna pĂ´de registar-se aqui e passar com sucesso pelo processo de registo escrito em inglĂŞs porque quis. Assim, poderĂŁo tambĂ©m anexar-nos traduções.
Cada vez mais fornecedores estĂŁo a oferecer boas ferramentas de tradução. Atualmente, o tradutor mais preciso Ă© DeepL.com, apĂłs um registo gratuito pode traduzir textos atĂ© 5000 caracteres de uma sĂł vez, sem registo ainda 1500 caracteres. Na parte inferior do seu sĂtio Web (secção inferior), encontrará aplicações para PCs Windows e Apple, para Android, ChromeOS e iOS, bem como extensões para as famĂlias de browsers mais populares, que tambĂ©m oferecem esta gama de serviços, e tudo Ă© gratuito.
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Também pré-escrevo quase todos os meus textos mais longos e traduzo-os depois, na maior parte das vezes à mão, mas com a ajuda de dicionários e, por vezes, até recorro a um tradutor de texto completo, especialmente quando estou cansado, doente, com pressa ou com pouco tempo.
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This is by agreement and stipulation in the forum rules, an English language website and every user is explicitly encouraged, if posting in their native language, which is absolutely fine, to add an English translation to their posts.
This is a practice that has worked very well in the forum, as it makes it possible to get a more likely accurate translation of a possibly unclear, inaccurate or unfortunate translation with the help of the original text and other translators.
This is nothing unusual here, but above all you make it easier for all of us to communicate with each other so that nobody can’t translate your native language texts due to a lack of language skills or computer skills and would be excluded.
You, who write here in your mother tongue, were finally able to register here and successfully go through the registration process written in English because you wanted to. Then you will also be able to attach translations to us.
More and more providers are offering good translation tools. Currently the most accurate translator is DeepL.com, after a free registration you can translate texts up to 5000 characters long at once, without registration still 1500 characters. At the bottom of their website (the lower section) you will find applications for Windows and Apple PCs, for Android, ChromeOS and iOS, as well as browser extensions for the most popular browser families, which also offer this range of services, and everything is free.
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I also pre-write almost all my longer texts and translate them afterwards, mostly by hand, but with the help of dictionaries and sometimes I even use a full-text translator, especially when I’m tired, sick, in a hurry or pressed for time.
Michelist
There is.
Selection → show global selectionmask
Now you have an additional layer/mask. On this mask you can draw with your brush (with black and white).