[KronisLV]

SSH/HTTP/3

That way, when you need to use sed for editing text containing it, your pattern can be more interesting:

  sed 's/SSH\/HTTP\/3/SSH over HTTP\/3/g'

[Wicher]

try:

  sed 's:SSH/HTTP/3:SSH over HTTP/3:g'

At least with GNU sed, you can use different separators so dodge the need for exscaping. | works as well.