From what I have actually seen with version 13 it Isn't all that bad, slash commands, etc. However, lots of the patterns are changed, for example:
" Channel types are now uppercase and align with Discord's naming conventions. "
What you'd put in V12 | - if(channel.type === 'text') channel.send('Content');
What you'd put in V13 | + if(channel.type === 'GUILD_TEXT') channel.send('Content');
Link about updating from v12 to v13:
https://discordjs.guide/additional-info/changes-in-v13.html#collection
Honestly, I wouldn't bother with the hassle of upgrading, V12 is better. Just seems out of place to use 'GUILD_TEXT', when you can just use 'text', simpler for the person coding. I'd heavily suggest V12 then V13.
Please let me hear other thoughts on the upgrade to V13 :)