If you’re going to send only occasionally, it’s probably best to use platform shared IP addresses. You’re somewhat at risk in that other people’s bad hygiene could affect you, but you’re mitigating the “cold IP” risk.

Honestly though, these types of blog posts are frustrating to read if one actually has knowledge about email deliverability. It’s so vague. I always wonder if it’s vague on purpose, i.e. they want to complain but they don’t want to admit dumb / bad stuff they did. In my experience Gmail is demanding but it’s not totally random or capricious.