For yet another time I was added to a telegram pump/signal group which I usually instareport and delete but this time I was bored and got curious : of course I didn't invest any single cent in it but decided to stay in the group until their deadline would expire; it lasted a week during which they were periodically sending reminders in "mooning soon" style. No one can write or comment in the group.
When finally the token was revealed I digged into it a bit but I have never been involved so much in erc20 tokens/smartcontracts and therefore my knowledge is limited.
I will advice you change the privacy settings of your telegram to avoid random people adding you into groups. I have been scammed before through that means, so I learnt from it by adjusting the privacy of my telegram account to allow me join group myself and not be added by random people or even bots.
What does that 99% sell tax mean? Does it mean token creator eats 99% of the sell price and only 1% hits the seller's wallet?
It means that if you connect your wallet to interact with their smart contract, they will drain your wallet from the tax and the other fees you see their percentages specified. It is definitely a scam setup to steal people's fund.
Some go as far as delivering the token to your wallet and you could see the price through onchain data collected by Coinmarketcap. If you attempt to sell the token in PCS or any other DEX, they will drain your wallet.
Therefore, I will advice you leave the group and never attempt to connect your wallet to interact with their smart contract. Finally, adjust your telegram privacy to avoid future recurrence.