Coinbase coins can't be transferred until 100 blocks after they were created.

(Why did you generate "101" blocks specifically?)

So, the amount in your wallet you see is from the first block you mined. You can verify that by bitcoin-cli -regtest getblock "<hash of first block>" which you had got in return to the generate 101 command you ran earlier (an array of 101 block hashes).

Try the following

• generate one more block bitcoin-cli -regtest generate 1
• now listunspent and you should see 2 utxos instead of 1.

Depending on what you want to test, maybe simply creating a new address and sending money to it is enough for you?

[Edit]

1. Shut down core properly.
2. Rename your wallet.dat file
3. When you restart, a new wallet(wallet.dat) will be created. You can use them by supplying -wallet arg to bitcoin-qt

For example, if you are on linux:

Create 4 wallets by starting bitcoin core, stopping bitcoin core and then renaming the wallet.dat in your ~/.bitcoin folder (then repeating the process). For example, run this process 4 times to generate :

• mywallet.dat
• wifeswallet.dat
• kidswallet.dat
• businesswallet.dat

Then, in linux, in your .bashrc :

alias mywallet="bitcoin-qt -wallet=~/.bitcoin/mywallet.dat"
alias wifeswallet="bitcoin-qt -wallet=~/.bitcoin/wifeswallet.dat"
alias kidswallet="bitcoin-qt -wallet=~/.bitcoin/kidswallet.dat"
alias businesswallet="bitcoin-qt -wallet=~/.bitcoin/businesswallet.dat"

You are creating a blank wallet which has no keys because of the third argument which is true.

1. blank (boolean, optional, default=false) Create a blank wallet. A blank wallet has no keys or HD seed. One can be set using sethdseed.

https://bitcoincore.org/en/doc/0.21.0/rpc/wallet/createwallet/