So I didn't find amiibo compatibility charts, but I tried to estimate them based on release dates:
- Wolf, Ridley, Inkling - December 07, 2018, so 1.0.0, base game or maybe 1.1.0, day 1 patch
- Piranha Plant, Ice Climbers, K. Rool - February 15 2019, so the closest update is 2.0.0, 2 weeks prior, which had Plant
- Ken, Young Link, Daisy - April 12 2019, so the closest is 2.0.1, without characters.
- Pichu, Isabelle, Pokémon Trainer - July 19, 2019, the last update being 3.0.1, post Joker, the update that fixed his Classic mode bug.
- Squirtle, Ivysaur, Snake - September 20, 2019, the last update being 5.0.0, with Banjo and Kazooie.
- Chrom, Simon, Incineroar - November 8, immediately after Terry, so 6.0.0
- Dark Samus and Richter - January 17, 2020. Thing is, latest patch was 2 months ago, so there's two possibilities: either they got added in 6.1.0 (November 14), which sounds unlikely or we're getting an update soon.
I'm not sure if they would add amiibo compatibility in minor, unnumbered updates, but... I guess it's also a possibility?