Electronic Music Open Mic nearest one is in Bournemouth, but there are standalone events in Southampton, like those run by Address Soton.
RE:PLAY Portsmouth - Rewilding the dancefloor Replay is a series of events that aims to rewild the dancefloor by recentering creativity, community and the environment through a love for electronic music.
South Coast Electronic Music (opens in a new tab) "People who enjoy electronic music as well as people who make and play it."