Minecraft Java Edition is for PC, MAC, and Linux devices. Minecraft Bedrock Edition is for consoles, Windows, and mobile devices.
Does what cost money? Minecraft is not free, but you can play a really old version of the game free at classic.minecraft.net.
There are several differences in servers because of differences between versions. For example, there is a command called /scoreboard that is way more sophisticated on JE than BE.
There have been many changes since 1.8. The current version is 1.17. Some major changes include shields, Netherite tools/weapons (which are not all standard crafting recipes), addition of copper and amethyst, addition of trees, new biomes, and new structures to the nether, piglins and hoglins, and many more.
If you're looking to quickly learn about recent changes, I would suggest you watch a couple beginner tutorials made recently (regardless of your skill level) to become familiar with new mechanics such as shields, new ores (and where they generate), and other major updates to the nether and overworld. Do note that in 1.18 the y limits will be changed from 0-256 to a larger size (including negative numbers) so any mechanics you learn now may change this holiday season.
- This is an opinion based question and therefore I cannot answer accurately. However, Googling this question consistently returns Hypixel.
For more general information on Minecraft and recent changes, see minecraft.fandom.com.