aiogram VS Telegram-To-Discord-Forward-Bot

The first idea is doable if you have programming skills. Maybe with something like this: https://github.com/aiogram/aiogram

It could be made to join groups, I'll really consider that if there is a demand. I'm using Aiogram bot and it support this.

Here, the decorators have already used filters built into aiogram. The entire list of such filters can be found here.

Of course, it's good to write API requests yourself. It reduces the dependency on third-party libraries and allows you to control the behavior of the code more. But when there are more such methods than twenty, it already increases the size of the code. It becomes difficult to manage all the logic. This is where third-party libraries(frameworks) come to the rescue. After choosing a language, you can consider the options of different libraries from the list here, on the official Telegram page. For JavaScript I recommend using node-telegram-bot-api and telegraf. For Python you can take pyTelegramBotAPI and aiogram(highly recommended).

you can start by looking at python-telegram-bot, pyTelegramBotAPI, aiogram. The rest is looking throught the documentation.

aiogram

I'd suggest not using pyTelegramBotAPI because of its unstable polling. If you're ok with asyncio, try https://github.com/aiogram/aiogram

I'm willing to release the code on GitHub along with an article on my blog if you are interested. The bot is coded in Python using mainly the Aiogram package https://github.com/aiogram/aiogram.

I have never used python-telegram-bot (which looks like to be your case), but with aiogram, it's pretty easy to send mediafiles: https://github.com/aiogram/aiogram/blob/dev-2.x/examples/media_group.py (you can replace "attach_photo" with "attach video"). Note that the latest aiogram version 2.12 seems to be broken, so downgrade to 2.11.2.

look into async solutions. https://realpython.com/async-io-python/ https://github.com/aiogram/aiogram -> aysnc telegram https://github.com/pgjones/quart -> flask replacement