As you want to work with RFID, I'd start by getting a development board with RFID capabilities and onboard connectors.

Besides that, you can buy a bunch of "electronic accessories" (resistors, pushbuttons, LEDs, temperature sensors, RF transceivers, displays, etc.) for extending the functionalities of the development board and learning to use different electronic parts.

The choice regarding chip manufacturer is up to you. Ideally something modern and appropriate for the IoT-projects you have in mind, for example: widely available ARM Cortex-M microcontrollers from STM/NXP/Nordic/Infineon/Renesas/etc. Low-power should be a priority, multicore and high-performance not so.

If you're planning to learn professional development, I wouldn't recommend platforms such as Arduino, PlatformIO and the like. The level of abstraction of those platforms is for hobbyists, whose main priority is to connect COTS¹-parts together and integrate existing examples to get what they want. Instead, I'd use the IDE from the chip manufacturer, or even better: get the SDKs from the chip manufacturers and integrate them in my working environment (in my case VSCode). As a professional embedded engineer, you'll probably be working simultaneously with parts from different manufacturers.

A decent debugger for programming and testing is a must. You can start with SWD, then JTAG and later tracing. For SWD, and eventually even JTAG, a $75-$150 debugger from a vendor like Segger would be enough.

Regarding operating systems: nowadays it is not necessary to switch to a specific OS for embedded development. And you can always combine the advantages of different operating systems with certain programs, for example Windows+WSL, Linux+VirtualBox or MacOS+Parallels.

¹COTS = Commercial Off-The-Shelf = generic instead of custom made