Some years back, when I was playing with the ATmega128, I was using Linux. I had installed avr-gcc, avr-libc and avr-dude (the programmer) and all I used for the IDE was 'gedit'. A simple Makefile had targets for 'make all', 'make program' and 'make clean'. For larger projects, dependencies can also be automated with 'make depend'.
All of those tools already exist in the Arduino directories. I haven't tried it but I suppose you could use the Arduino IDE and none of the Arduino specific libraries.
Or, you can spend the time to install Eclipse. Microsoft Visual Studio will probably work and, as just an IDE, Visual Code works pretty nice. There may be a plug-in to allow programming, there are a lot of plug-ins for Visual Code and Eclipse. If not, keep a console open and just use avr-dude directly (probably through a batch file so you don't have to keep typing all the options).
I have't used Visual Studio for ATmega projects in a long time but it used to work well. I was adding switches, knobs and dials to Microsoft Flight Simulator using the Windows SDK and the tools for an ATmega <something> all in the same session. I could compile and test the C++ code for the PC and compile/program the ATmega code all from the same IDE. No, I don't remember how I set that up but it worked well.