Migrating Filetype autocmd setting from vimscript to lua

I'm migrating my vimscript settings to lua, but hit a snag.

I got several of these type of autocmd settings which I don't have a clue how to migrate them

augroup py_fold_custom
    autocmd!
    autocmd FileType python setlocal foldmethod=indent
augroup END
augroup html_syntax_disable
    autocmd!
    autocmd Filetype html if getfsize(expand("%")) > 500000 | setlocal syntax=off | endif
augroup END

Can somebody help?

Good choice switching to neovim. I know how it feels overwhelming to translate these sort of commands. While most of my config has been converted, I have one huge monster vim script command that I've yet to be able to translate.

As with everything in neovim you have several options of how to convert these to lua.

First, using autocommands

local generalSettingsGroup = vim.api.nvim_create_augroup('General settings', { clear = true })

vim.api.nvim_create_autocmd('FileType', {
    pattern = { '*.py' },
    callback = function()
        vim.opt.foldmethod = 'indent'
    end,
    group = generalSettingsGroup,
})

vim.api.nvim_create_autocmd('FileType', {
    pattern = { '*.html' },
    callback = function()
        if vim.api.nvim_buf_line_count(0) > 500000 then
            vim.bo.syntax = 'off'
        end
    end,
    group = generalSettingsGroup,
})

But you could also use the ftplugin directory for things like this.
You can still use lua, and upon detection of these file types this code will be run by neovim just by being in this directory.

In a file in your config directory create ftplugin/python.lua with this in the file

vim.opt.foldmethod = 'indent'

And for the html one ftplugin/html.lua

if vim.api.nvim_buf_line_count(0) > 500000 then
    vim.bo.syntax = 'off'
end

Those are the main ways that come to mind for me. I hope this helps!