note: OP also opened an https://github.com/spesmilo/electrum/issues/8419, where I replied in detail.
In short,
- when you open a channel, you cannot receive before sending some first
- and it is the channel-opener who pays for the on-chain fees of having the channel closed in the future, for which part of the opener's balance is set aside. When the on-chain fees are as high as recently (~500 sat/vb), the fee set aside can easily be approx 2 mBTC.
As OP opened a channel with a capacity of 2 mBTC (the minimum hardcoded value allowed by Electrum), he basically had no usable balance left.