The Etherington Brothers - they have produced 300 tutorials on how to draw, 200 on writing and are still making more! Plus you can read the first chapters of their books for free.
The Tea Dragon Society by Katie O'Neill can be read in it's entirety online
If you fancy combining comics with learning try Dekko Comics - you can read them online for free and browse by subject.
Robert Louis Stevenson’s horror story The Tale o Tod Lapraik (comic drawn by Gary Welsh).
If you enjoy non-fiction you can download a pdf of John Muir, Earth – Planet, Universe
The Book of Hopes - a free to read online this collection of words an picture by the UK's top illustrators and writers.
Free Comic Book Day e-comics from past years on Comixology (search for 'Free Comic Book Day') Or DC Comics have a made a bunch of comics free until June.
You can download a copy of the Beano for free.
Webcomics are usually passion projects so the topics, quality and frequency vary hugely. Some are professional artists sharing their work with the world and using other avenues to make money from their art or writing a webcomic as a side project. It's worth trying a variety to find the ones you enjoy, plus as the ones I am suggesting have got pretty hefty back catalogues to read through.
There are lots of webcomics I really enjoy reading, these ones are all still on going:
Breaking Cat News is cats telling us the news.
Slack Wyrm - is about a very lazy dragon
JL8 - imagines the Justice League at age 8
Heartstopper - LGBTQ+ teens in high school
The Flying Ship - LGBTQ+ fantasy quest
Phoebe and her Unicorn - one girl and her unicorn
Dinosaur Comics - t-rex deals with life
If you are a library fan then you can also give Unshelved or Library Comic a go both of which I really enjoy, though I fear they may be funnier to those of us who work or volunteer in libraries.
If you are still looking for more Book Riot produced a list of 50 they'd recommend or try Hiveworks Comics or Tapas both publish a wide range of webcomics you can read for free.
I love a daily comic strips like you'd find in newspapers by professionals as well. If you fancy those you can find comics like 'Garfield' and 'Peanuts' can be found here on GoComics . They also have the wonderful 'Calvin and Hobbes' and 'Get Fuzzy' both of which you can read the complete the collection. You can pay a subscription but you can also just read them for free on the site.