Valheim is doable solo but playing in team consistently lifts alot of grind that otherwise would pile or force to skip as much on the way up tech tree. And off course - early access things like mechanics that need alot of polish (combat/mobs behaviour for example) or areas waiting to be impemented or filled with content. Recent news speak of caves (dungeons) for mountains going through tests but still weeks from being ready for main branch if i got it right.
Can say anything about Astroneer cause never tried or heared about it.
'When in doubt - take game in 1.0' is reliable way to pick but if its more about appealing aestetics and beardmen in helmets caught you eye Vallheim does viking thing quite well. Building and decorating base (at least wooden and iron elements) works well and looks good.