There are decades and there are decades. Just like there are weeks (period between Monday and Sunday inclusive) and weeks (any seven consecutive days).
When you say “I’ll do this next week”, then you mean the next period between Monday and Sunday. When you say you’ll do it in a week, it means you’ll do it after exactly 7 days from now, regardless of what day is it today. Same for decades.
There are decades and there are decades. Just like there are weeks (period between Monday and Sunday inclusive) and weeks (any seven consecutive days).
When you say “I’ll do this next week”, then you mean the next period between Monday and Sunday. When you say you’ll do it in a week, it means you’ll do it after exactly 7 days from now, regardless of what day is it today. Same for decades.
You said start of a new decade, not the new decade in the original comment, they are very different
??? You know very well what I meant, be more forgiving to second-language speakers
when I originally replied to you, I very obviously did not know that you meant that
didn’t know you weren’t a native speaker either