[helene_t]

6-9 doesn't sound like 21st century. It goes back to the 16-18 range of of the 1960s. 1nt then is to play opposite 13-15.

[dokoko]

I am always impressed how people can make a simple matter complicated.

If you have 6-9 pts without sufficient support for partner's suit - as the OP suggests - you are clearly worth a bid but not at the 2-level. So either you have a suit you can bid at the 1-level or you have to bid 1NT (with or without stoppers, balanced or not).

When partner opens 1♣ and you are entitled to raise on 4-card support, there is always an in-between suit you may bid so with unbalanced hands you bid that suit and with balanced hands you have a choice (you may then play 1NT to show stoppers or a narrower point count).

In responding to partners opening on the 1-level you may bypass a 4-card (or even 5-card) diamond suit but you should not suppress a 4-card major as partner isn't invited to introduce a major on the 2-level without considerable extras and an unbalanced hand. So if you don't bid your major it's likely to get lost.

You may, however, do as you like. If you want to suppress your major, pls do it against me.