There are commands such as
:Continue, but I would like an
:Until to run to the current line without setting a breakpoint. Is it possible to add this myself, or would it need a vim feature request?
It's documented at :h termdebug_shortcuts
nnoremap ,u :call TermDebugSendCommand( printf( 'until %d', line('.') ) )<cr>
It's add at patch 8.1.0071 .
Tons of bugs have been fixed since 8.0, update to 8.1 or 8.2 if you can.
If you want to stay in 8.0, you can try to replace your termdebug.vim with master version, it's located at
$VIMRUNTIME/pack/dist/opt/termdebug/plugin/termdebug.vim, note that you should back up the original version, I'm not sure if it would work.