As @astra_the_dragon mentions, the journals also accept Markdown syntax, similar to comments on the forum. It’s easier and simpler than HTML & takes only ~60 seconds to learn.
A great tool for writing Markdown documents is Obsidian. It’s free for personal use. If you want something lightweight, StackEdit is an in-browser MD editor & viewer.
For tables, use a spreadsheet program, then paste a selection from your spreadsheet in this Markdown Tables Generator to convert into Markdown code, which can be pasted back into your document or journal. Here’s an example of a journal note I wrote to help me quickly explore photos of local moth species that I made using the same process.