The most supported version is 1.21.0 (Note: not 1.21.1) with 23 usages. This is because BetterConfig, on Modrinth, does not support 1.21.1, and CompleteConfig is the only library to not support 1.21.0.
After that, 1.21.1, with 22 libraries supporting it, and at third place a 7 way tie between 1.21.11, 1.21.9, 1.21.8, 1.21.7, 1.21.6, 1.21.5, and 1.20.1, each with 21 usages
Then, 1.21.10, 1.21.4 and 1.21.3 have 20 usages (YAML Config does not support these, hence why they have one less supported lib than the other 1.21 versions)
At 19 supported libs are 1.21.2 and 1.20.6 (Forge Config API Port does not support 1.21.2) (I couldn't figure out the sole library not supporting 1.20.6)
I could continue, but I'll just put the entire list here (Note: I will assume that the 26.1 versions are off, because I don't know they are updated yet):
| Versions | Count |
|---|---|
| 1.21.0 | 23 |
| 1.21.1 | 22 |
| 1.20.1, 1.21.5-1.21.9, 1.21.11 | 21 |
| 1.21.3, 1.21.4, 1.21.10 | 20 |
| 1.20.6, 1.21.2 | 19 |
| 1.19.2-1.19.4, 1.20.0, 1.20.2, 1.20.4 | 18 |
| 1.18.2, 1.19.0, 1.20.5 | 16 |
| 1.19.1, 1.20.3 | 15 |
| 1.18.0, 1.18.1 | 13 |
| 1.16.5, 1.17.1 | 12 |
| 1.17.0 | 11 |
| 1.16.0-1.16.4 | 8 |
| 26.1.x | 7 |
| 1.15.2 | 6 |
| 1.14.x, 1.15.0, 1.15.1 | 5 |