[Koshkin]

Colour Maximite is a lot of fun [1]! The BASIC environment it has is quite powerful, and it even runs a full-screen text editor.

[1] https://www.youtube.com/watch?v=XQA8lowEKOo

[bartread]

Beat me to it: I was going to post a link to the 8-Bit Guy's video as well.

There are, I believe, various versions available and if you just want something to learn and write BASIC programs on it's difficult to imagine a better place to start because it boots directly into a BASIC prompt, just like 8-bit microcomputers from the 80s.