It is the best answer at the moment. You can keep an absolute basic phone with all the banking and such apps loaded and nothing else. You treat it like an appliance. Your daily driver will be separate and can be running PostmarketOS or LineageOS etc.
There are several benefits off the top of my head:
1. Since you only install banking/govt type apps on your "important" phone, it stays more secure vs. putting your random game app along with the banking app on the same phone.
2. When you upgrade your daily driver, you don't need to deal with tons of re-auth steps for banking/govt apps.
3. Your daily driver can be customized to the nth degree because the pesky banking app won't be on it to refuse login because, say, you turned on developer options or rooted the phone.
4. You can even leave the basic phone at home for extra safety, if you wish, without affecting your daily driver.
5. You can root your daily driver and put as much adblocking setup as you want to boost your privacy. Your basic phone won't have enough activity outside banking/govt. to build much of a profile.