Use an mfa app which supports import/export of backups. To name atleast one popular open source example: Aegis.

Do backups, than you can always fairly easy and fast restore your backup after loosing a device. Usually thats enough as in most (not business relevant use cases) you do not need mfa within minutes.

If you want to go one step further you can prepare an old phone with your mfa data and store it in anywhere in your flat/house and use it as drop in replacement after loosing your actual phone. Or you could setup your mfa app on a seperate phone of your mom/friends/son/daughter, if you dont have an old phone lying around.

I am using Cospend together with my nextcloud. There is an Android app (Moneybuster) and iOS app (PayForMe) aswell. Worked quite nice so far.