Readme for pack.mcmeta
The most interesting Thing in this file is the pack_format entry.
pack_format list for Minecraft versions:
1: 1.6.1–1.8.9
2: 1.9–1.10.2
3: 1.11–1.12.2
4: 1.13–1.14.4
5: 1.15–1.16.1
6: 1.16.2–1.16.5
7: 1.17-1.17.1
8: 1.18-1.18.2
9: 1.19-1.19.2
(Most likely you will only ever use 6 and later because there is no FSB mod for earlier versions)