A new source was added to my account without my asking, namely "D&D Free Rules (2024)". I don't want this and it is breaking all my current campaigns and character sheets.

I own a lot of content from 5E and all my currently running campaigns are running 5E. I have no intention of switching any of them to 2024, however all of my characters and the characters of my players are now being forced to show and use 2024 rules even when using Legacy classes. New 2024 spells show in the spells list and changes to rules have been implemented into the character sheets. 

This has made content I paid for completely unusable as it's a nightmare to differentiate between what is legacy content and what isn't. For example, Tasha's should show as legacy as it was made for 2024, but doesn't because apparently it's compatible with 2024 rules (atleast until a new sourcebook is released that overrides Tasha's). In reality all sourcebooks for 2014 should be marked legacy and a clean change done. There should then be an option to select 2014 or 2024 rules when creating your character, any 2014 sourcebooks compatible with 2024 could then show in the 2024 selection anyway.

I do not own any of the 2024 books, and because they were so extortionately priced I have no intention of buying them at this time. On top of this, a lot of the new rules seem poorly designed, particularly around spells. 2024 is in reality 5.1 and charging hundreds of pounds to have to buy all new books is just absurdly exploitative. We should be able to use the content we already own without being forced to use the new badly designed rules being forced upon us. I will be cancelling my Master Tier this month and will not come back unless significant changes are made to DND Beyond. This used to be the best DND resource on the internet, and now the free options are better as they respect people and their choices.

How you want to play isn't any of my business but you seem to be confused about a couple of things.

The "Legacy" tag has more to do with whether something has been replaced by a newer version than whether it's from the 2014 or 2024 rules. For example, the Goblin playable race from Mordenkainen Presents: Monsters of the Multiverse uses the 2014 rules but isn't tagged as Legacy. It replaced the Goblin playable race from Volo's, so that one is tagged as Legacy.

Anything from the old books that wasn't updated is still compatible with the 2024 rules. It makes no sense to mark entire books as Legacy; they're not obsolete.

I still have lots of character sheets made with the 2014 rules and they're intact from what I can tell. My Artificer still has the 2014 version of Cure Wounds prepared, not the 2024 version.

Yep. The only things that are changed on old sheets are tooltips and a couple of names, like Heroic Inspiration replacing Inspiration. (The exception to this is system bugs they're working on, like the Monk damage die.)

2014 characters are still fully playable as-is.

Some have found the new stuff not so much as a bother as others have, I have 3 tables that are looking to other systems over this, and 2 that really don't care. All of them have lost play time over this and that is very annoying. I now have to learn at least 1 new game over this if not 3 depending on what each table settles on. This is very frustrating to me as I spent lots of time recruiting the players at the 3 tables leaving DDB over this and would prefer they stay. Why won't wizbro put a freaking toggle on the 24 rules?!

The sheet is also missing the legacy rules for Initiative, Inspiration, Unarmed Strike, Grapple and Shove, and in the case of Unarmed Strike the 2024 rules are prominently displayed on the Actions tab whichever rules you want to use.  I've not yet seen any official acknowledgement* that this will be fixed, so for now I do not consider the sheet to be "unchanged".

That's on top of the bugs (monk dice, Aid on clerics and druids etc) that have been introduced and are intended to be fixed, but are no doubt much lower priority than any of the new stuff.

*the mods on discord have passed the info on, but there's no feedback of what DDB actually consider a bug to be fixed

Since this and other issues have topics popping up for weeks, i dont think they will fix it or that its bug.

More like feature following theri intention to 'leak' 2024 edition everywhere and to make using originall 5e as paintfull as possible

I played tonight in a 2014 campaign and after level up 2024 free rules have started overriding base 2014 rules in my character, like weapon damage in addition to the items mentioned by DCTrekkie.

Also having this issue with my new players characters as well as my own. it is extremely frustrating.

Sadlly we have to deal with it.

I kinda surrenderes already and while i dont use 24e mechansics but i did accept stuffs what DnDB forcing ne to.

If new player joins your 5e campaign you have to watch over him to make sure he gets 5e character as 24e would be probably OP in comparsion to 5e (that could be problem if you would have one class twice in different edition in xour group)

You can tell your players to only pick spell marked as legacy but somebwithout 24e version arent marked that way so its better to jump for new versions

You absolutly dont have choice about abilities or weapon dmg and so. Nothing tu do here except 'remeber that this ability actually doesnt do what it says' which would be worst solution imho

Weapon mastery is just text so you can ignore it. I use it as critical hit effect (you will need modify some)

For sure it would be better to just have option to turn off 24e, but..