I’d say that if a user makes no UK transactions for 6 months+, there is a reasonable argument to be made that they stopped being a UK resident (as defined by spending 6 months or more in the country of residence) and so are no longer eligible for an account.
That said, 2-3 months is well short of this, and I don’t think banks actively monitor for this either. And if you were planning to be gone for 6 months or more you could always explain and see what the bank suggests
In order to remain a British resident there are some basic tests such as do you own UK property, will you be in UK for at least 14 days in a tax year.
I travel outside UK for over 6 months sometimes and Monzo has not queried my account. I hope this continues.
Safe travels