I've installed a single app with 1G+ from Google Play Store in island without any issues. So I can confirm you it's no problem to do that in island.
The other workaround could be installing the desired app from mainland and clone to island with island app.
By the way, HTC U11+ stock android 9.0 here. Root with Magisk 20.3.
Currently, I cannot put it on the main space and clone it, because the application that I want installed, isn't free. And I removed my google account on the mainland. (the google play is only in the island).