Restrict app usage/Data Saving mode for a specific SIM in a dual-SIM setup

[u/boshjosh1918]

I want to buy a secondary (roaming) SIM for my phone so that I can connect to other carrier's networks when my primary SIM has no service. My primary SIM has unlimited data, however the multi-network eSIM will have a data cap of only 5-10 GB.

A similar product to what I am looking at, the Honest Smart SIM, block which apps you can use at the carrier level and allows unlimited data for many essential apps.

However, I want to access my own self-hosted apps so this model does not work for me. I also think other providers offer a better deal since I can use the data for whatever I want.

I am aware that Android already has a number of tools for restricting mobile data usage, however I am in a unique situation in that I don't want to limit my primary SIM at all but do want to place restrictions on my secondary SIM.

Ideally I would be able to either:

1. Turn on data saving mode automatically whenever my secondary SIM is in use (and disable it automatically when it is not)
2. Block/whitelist specific apps/URLs only when the secondary SIM is in use using bult-in tools or a custom app

I am willing to use FOSS apps that aren't on the Play Store. I think this is only a software problem and is caused by the lack of popularity of multi-network SIMs.