What’s the safest way to convert a relatively large amount of USD cash into Bitcoin for long-term holding?

Hey everyone,
I have a relatively large amount of USD in cash, and I’m considering converting it into cryptocurrency, mainly Bitcoin, as a long-term investment.
I’m still relatively new to crypto, so I’m trying to understand the safest and most reliable way to do this, especially since the amount isn’t particularly small.
I’d like to know what options are available for converting physical USD cash into Bitcoin, which platforms or services are trustworthy, and what the best way to store it securely for the long term would be.
I’m not interested in day trading or making quick profits. My main goal is to hold the funds in a digital asset rather than keeping them entirely in physical cash.
I’m based in Egypt, so I’d also appreciate any advice regarding local regulations or experiences with this process.
Would appreciate any genuine advice from people who have experience dealing with larger amounts. Thanks