Tip for US citizens with prior US earnings and a 401k already set up: When earning overseas, convert your existing IRA to Roth as much as you can, while using the 2555 exemption for your overseas earnings. [I wish I had known this twenty years ago!]
For any US citizen: unless you're committed to retiring in your current country, contribute as much as you can to an IRA and RothIRA, and place that in a generic index fund for best reliable results. Set aside your annual (or termination) bonus for that contribution.

Yes, buy rental property, passive income, etc. etc., any number of TikTok advisers can give you that advice, but that's hard to activate.