I’m not a native German speaker, but I agree with Akeri (thumbs up): “(vokalisches R) ɐ - it's called 'a-schwa’” lerner /leɐnə/. As far as the “normal” schwa, with no R timbre, I noticed that most German speakers (especially in the south) pronounce it as a somewhat neutralized /e/, that is, between /e/ and /ə/. This subtle difference is important in German. In reality, the schwa generally has a different timbre in different languages, for example, a French “schwa” actually sounds a lot like /ø/ (German ö). In English, the word “American” has /ə/ or /ɐ/ in the first syllable, but usually /ɨ/ (schwa with some /ɪ/ timbre) in the final syllable (because of assimilation to the N).

Actually, the IPA sign for the '-er' ending is ɐ - it's called 'a-schwa'. It sounds very similar to a (German) a, at least to a German. But instead of reading explanations, why don't you go ahead and listen to it? The ending -e is pronounced /ə/, that's correct. So, it should be /leɐnə/, I guess.

I’m not a native speaker but living in Germany that is a good reference. What I do is try to say Air for Er but with my tongue to the bottom of my mouth, not touching the teeth but below them right in front of the gums. If that makes sense.