Platformio and barebones ATTiny85/Atmega

Hello people,
Although I’ve done some work with arduino, I’m fairly new to embedded development and I have some concepts that I have not grasped yet.

I’m trying to program an ATTiny85 chip WITHOUT using the arduino library.
Will I manage it by using this connection diagram and and USBTinyisp?

What kind of setup does platform.IO needs for programming a barebones microcontroller?
Do I need a bootloader for that (I’m assuming that no, because a bootloader is a program that enables the chip to be programmed with other methods apart from a ISP like usbtinyisp)?

Forgive me if these questions have been answered but I searched and I didn’t manage to find a tutorial or something for that kind of programming, everyone want to use the arduino library.

Thank you

The topic Pure AVR Assembler programming discusses methods for programming an ATTiny85 using an external programmer and no arduino framework (AVR assembly). USBTinyIsp is also supported per Atmel AVR — PlatformIO latest documentation.

No, you do not need a bootloader, as your assumption is correct. ISP/ISCP programming does not need a bootloader. A bootloader is required if you want to upload via UART/Serial/some other communication method.

Pinout looks fine (you may find this one a good one to use, as it lists the alternate functions of the different pins). And as Max said, programmer is a supported one, so you should be good to go.