Could not find an option to Weld/Merge two separate nodes belonging to two separate paths.
UX : Something like
Click one Node in one path
Press Shift to extend selection
Click another node on another path
Then UI either
Weld Icon tool activate > Click = Merge all in position of last node Selected (*)
Right Click option (but this introduces a new behavior/UI) Option to merge at First or Merge at Last
Keyboard Shortcut ( (but this introduces a new behavior/UI) : merge at [F]irst or merge at [L]ast
(*) current sequence for all icons is "pick a tool then pick a node". This cannot easily apply for welding so Icon should not be active until at least two nodes have been selected and the welding can be applied
BecOzIcan
commented
3 years ago 
Could not find an option to Weld/Merge two separate nodes belonging to two separate paths.
UX : Something like
(*) current sequence for all icons is "pick a tool then pick a node". This cannot easily apply for welding so Icon should not be active until at least two nodes have been selected and the welding can be applied