How many shared interests do compatible couples need?

At least one or two strong ones (shared values, life goals, humor style). But having different hobbies is healthy and necessary. Research shows couples who do some activities separately (friends, sports, interests) are more satisfied than couples who do everything together. Separateness reduces codependency.

What if we have almost no shared interests?

Workable if you have shared values and enjoy spending some time together intentionally. But you'll need to build activities you both like: travel, cooking, volunteering, hiking. If you have zero overlap and zero desire to find any, you might be incompatible. Shared interests create bonding opportunities.

Is it a red flag if your partner doesn't support your interests?

Very much. Compatibility includes respecting each other's passions. A partner who dismisses your interests as "stupid" or demands you quit hobbies creates resentment. Healthy couples encourage separateness: "Go to your pottery class; I'll be here."