What apk arch to choose when there is no v8a, v7a or arm64?

There are some apps I get through Obtainium that have no arm-v8a option.

What should I install instead, arm-v7a or arm-64?

Officially afaik my OS doesnt even support v7a but 64, but until now I always installed v7a versions.

Which apps? Many of us use Obtainium so maybe can let you know which arch they use.

arm-64 is v8a, so choose that.