unlocked first of all, please stop relying on ChatGPT to answer your questions, you should do proper research yourself to get unbiased information. Besides, it's been proven multiple times that blindly relying on an LLM's suggestions can and will cause you harm.
Now to answer your question: Whether something is a risk or not depends on your threat model. From a security standpoint, using Instagram is harmless. Android sandboxing (and Graphene's hardened version of it) will ensure that no matter what happens, the rest of your device will not be affected (unless of course a sandbox escape vulnerability is found in which case things will get serious for every app). If you're paranoid about security, you could even use it in another profile, but you'll most likely have zero gains from that.
Totally protecting yourself from spyware like Pegasus is impossible because it relies on zero-day exploits, but using hardened, regularly audited apps can really help you, alongside GrapheneOS's secure base. The more you can avoid coming into contact with external, untrusted data, there are less chances that you will be affected. The usual security advice of not clicking random links, being careful with what you install and where from, etc. applies here too. Frequent reboots can also help clear spyware and are a good security practice.
If you're concerned about privacy, yes Instagram should be avoided. Meta collects tons of data about you through very invasive tracking. Don't give the app too many permissions (e.g. microphone, I use "only this time" to let apps I don't trust to make a call or something) or just completely abandon it. You'll be free of an addictive app that controls and uses you.