1
Some LND wallets provide a channel's "Number of Updates". Here's an example from Zap Desktop:
The LND gRPC API Channel Reference cites a property called num_updates. The description of this field is not very informative:
The total number of updates conducted within this channel.
What specifically is a channel update?

Updates can include changes to (on-chain) transaction fees. By default
num_updateswill also always be>0if the channel is fully established, because there is a required update between the channel's initial funding and the funds being locked. – Mark H – 2019-04-19T12:56:26.640The
num_updatesmetrics are also not 1, closer to 10. – kekcoin – 2019-04-19T13:45:46.847