Okay this is annoyingly clever

There is a honeybee statblock in Wilds Beyond the Witchlight. Also a regular spider in the Monster Manual, which could work just as well. Apparently the average spider in the Forgotten Realms is poisonous enough to have a 15% chance of immediately killing an average commoner with a single bite

I’ve done this on my Druid but with 3 portable holes..and the entire party.

There isn't anything to "deal" with. If you want your players to only give predetermined solutions to problems, you really need to play a different game.

If you've got the right DM for it, they lean into it, because everyone's having fun.

If you're not a fan of this type of behaviour, I recommend playing a TTRPG that isn't D&D.

D&D has gotten a bit of an "LULLZRANDOM!!11!!" reputation, possibly because of the content creators needing something whacky to get views, or just because of how mainstream it is. If you need to stand out in a crowd of thousands being extreme, novel, or whacky has the lowest effort for the highest reward.

If everyone at the table finds the game fun, then you are playing correctly. I find this behaviour exhausting and would tell the players that it needs to stop unless someone else wants to GM.

Imo this is firm "you can get away with it exactly once" territory. It's clever, so it should be rewarded. But after the once every lord will mysteriously have anti-shape shifting wards.

Personally I think the players coming up with some cool new trick for each encounter sounds pretty good. The problem is when they find one cool new trick that works for everything. Like, casting Create Water in someone's lungs sounds awesome the first time you do it, but you don't want a whole campaign of just that. But even if the players agree that that would be boring, it's hard not to do that without justifying why it wouldn't work, and if it wouldn't work every time, why would it have worked the first time?

Strategically placed near every door, window, sewer pipe, and vent the DM put an Antimagic Field device.

I once played with someone who argued that Diplomacy would never be usable on any important person because, since it requires 1 minute of uninterrupted conversation to use, everyone who is important enough would have a jester or aid or someone they'd hire specifically to interrupt every conversation they were involved in every 9 rounds. Absolutely infuriating person to play with. This anecdote is completely unrelated to this post, but your suggestion just made me remember it again, and it irritated me all over again.

A permanent channel of a spell of that high level I would hope would only be available to the most powerful of people.

Also those things would be so expensive they would be worth stealing!

I personally have two mages at entrances that are taking turns ritual casting detect magic. I guess similar impact, but it's not on all entrances.

I'll be damned, I wouldn't have thought wild shape was magic but indeed it is.

Antimagic field is an eighth level spell with one hour concentration duration; an item that has it on 24 hours a day would easily be a legendary item. People underestimate how powerful a spell it is and suggest spamming it everywhere. Having it on every door, window, sewer pipe, and vent would be massive overkill just to spite wildshape.