Is it because I’m the youngest?

It sounds like they gang up on you. How horrid.
They may be jealous of you but family dynamics are interesting. If it's any consolation, my in-laws call their youngest "the kid". she's almost 60 with teenaged DGC.

You don't need their approval but it isn't kind to put you down.

I notice teasing in our family WhatsApp group too and accept it but one of our DS is a joker and his siblings don't find it funny. I get accused of cheating in the quiz. We are mostly in agreement on politics, luckily.
Is it video or texts?.
Our group is just our DC. I don't have a group with my siblings. Life's too short!

Have you spoken to them individually to tell them that when you post stuff you would welcome kinder comments from them as these are important hobbies for you?
They sound a bit insensitive and I wonder if they are closer in age to each other than you you?
Other than that as others have said just mute the conversations and perhaps don’t post much stuff, they may get the message!

leave whatsapp, I have 5 younger siblings, one from aus was being very derogatory about the uk and I am defensive about the uk, rather than me becoming snipey, I left whatsapp, not in a huff but to avoid any confrontation with this particular sister. We are all close but saying things from aus having had a few drinks in the evening can make words come out in a wrong way, like e mails

Your choice, you don`t need to be there

Sounds to me like they are a bit jealous of you? Do you think this can be true?
Anyway I would take Jane10's advice.

Why not 'mute' the conversations? You'll not be alerted to a new message but they'll all be there if you want to read them. If you don't respond much they'll maybe get the message?

I think being the youngest can mean you are fair game for older siblings to 'tease'. It's the habit of a lifetime. They somehow forget you have grown into an adult too and if you live far away, they don't see you that often, so you are still the 'baby'. Just say what you need and ignore any unacceptable comments. Take care from another 'baby'.

Rant away. Sometimes we just need to vent.