Welcome! It’s great to have you. My first PC was a 386 SX as well, although running only at 16 MHz. Luckily by the time Doom came out it had been upgraded to a 40 MHz 386 DX, which was just barely able to run it!
Sadly I didn’t have as cool a machine as your Atari ST before that. My first computer was a Sharp MZ 731, which is a sort MSX-type computer from the early 80s. By the time I got it in the late 80s, it was very outdated already. Still had fun playing some games from the built-in cassette player, even if it sometimes took 20 minutes for a game to load haha
Anyway, welcome to the club and I hope to see you around, either on the forums, in the chat room, or maybe through a voice message or as a podcast participant.