Generally, international roaming is a lousy value. It’s far more cost effective to secure short-term service locally (in country) or, if data alone is sufficient and one’s phone is eSIM capable, using something like Airalo (or one of its competitors).
If one has a dual SIM via eSIM capable phone, one may temporarily add local cellular service without disturbing their current U.S. service and may be able to access their U.S. service using VoWiFi (carrier WiFi calling). With some phones, iPhones in particular but also many Pixels, VoWiFi will also work over local (in country) data service.
I appreciate you are aware of this as evidenced by the solution you offer in the referenced A Solution for Canadian Roaming Worthy of MacGyver. That solution, however, pertains to a narrow circumstance. I believe OnePlus may be the only brand offering dual physical SIMs in the U.S.