Portfolio advise for a flexible residency between Europe and the US

Hi all,

I am a

  • 33 years old Tunisian citizen (holding only a Tunisian Passport for now)
  • Living for the past 5 years in the US, under a J1, some years I was tax resident, and some years not, depending of the substantial presence test.
  • Since last year, I applied for and I got a freelance/investor residency card in Portugal and got the Non Habitual Resident (NHR) tax regime (no tax on foreign income for 10 years).

On the short term (next 2-4 years), I am planning to return to the US under an O1 visa, and work for the US government (CDC); again, some years I will be a US tax resident, some years not, depending of my travels. In the meanwhile, I plan to keep my residency in Portugal and eventually apply for a Portuguese passport (I will lose the NHR status once I get the Nationality), and move permanently to Europe.

I have over 130k of saving that I want to invest, and I am looking for a simple passive investing strategy, using a portfolio of accumulating index funds / ETFs that I would set once and forget about. But I am struggling for a long time now to identify the best investment strategy given my flexible and unpredictable tax residency.
Questions I am thinking of are
investing from Portugal vs investing from the US?
Ireland domiciled ITFs vs US domiciled?
Possible brokers to use?

I have looked at many forums such as blogleheads: https://www.bogleheads.org/ ; index fund investor europe: https://indexfundinvestor.eu/ ; retirement researcher: https://retirementresearcher.com/ ; and this ETF domicile decision table: https://www.bogleheads.org/wiki/Nonresi … sion_table ; but did not find anything that was specific to my situation.

In the short term as I will be a US tax resident, it seems that it would be better to invest from the US in US index funds. But that strategy does not seem to fit best my long term European residency plans.
I though maybe it is better to invest from Portugal since now in Ireland domiciled funds, and keep them accumulating during the 2-4 years I will be in the US, but was not able to Open and account with Degiro or Interactive Brokers because I was a US tax resident in the past and I could be one again in the future.

At this stage, I read so much on the topic without success and am so desperate that I totally fine paying for an expert advise. I am at the stage of thinking that what fits my situation best would be to

  • invest from the US in US domiciled funds during the 2-4 years I will be there
  • Cash out everything once I leave the US and move to Portugal (no capital gain tax in the US as I will not be a US resident, no capital gain tax in Portugal as have the NHR status, or am I missing something?); then
  • reinvest everything from Portugal to an Irish domiciled fund…

but that does not seem ideal, plus what would happen if I decide to return again to the US for some years?

Since this will be my first investment experience, I am scared I am missing something obvious?
Any idea on how to strategize long term investment for flexible residencies between Europe and the US?
Or recommendation for a Portuguese-US expert tax/investment advisor?