I'd like to know if this piece I wrote is understandable?.

I woke up at 9:30 am, a little late, and stayed in my bed until 10:30.

I was feeling very lazy but I managed to reunite allgather my strength toand get up off myout of bed.

"Gather my strength" here is perfectly natural and correct but carries a connotation of tongue-in-cheek exaggeration FYI. Still fits perfectly though.

Today is Brazil's independence day holiday.

We celebrate Brazil's independence ion September 7, but this year it's going to be different because protesters will take the streets in many capitalmajor cities to protest against the supreme court and to show support for the president Bolsonaro.

There is only one capital city per country, every other big city is just big/large/major city. For example, the capital of the U.S. is Washington D.C., the capital of Brazil is Brasilia (but you know that).

Opposition politicians, journalists and the media are concerned about theses protests because many of Bolsonaro's supporters defendsupport a military coup and the removal of supreme court and parliament.

Not up to date on Brazilian politics, so excuse me, but you can only use "defend" if the coup has already happened, in which case you might say "... supporters defend the military coup ..." Also be aware of your omission of the Oxford comma in "politicians, journalists (would go here) and the media." It's not wrong to not have a comma as long as you understand that sometimes it might be required by a teacher or something.

Bolsonaro himself ion many occasions, in hias speechs, threatened the supreme court in his speeches.