Internet dongle for MacBook Air 2024?

If you mean cellular internet access, then you can choose from:

• personal hotspot* from your iPhone or cellular iPad,
• hotspot device [4G/5G] (for potentially multiple devices) from a UK local ISP** with local SIM or eSIM,
• USB dongle for laptop (one device at a time) from a UK local ISP** with local SIM or eSIM.

*As roaming charges abroad can easily get out of hand, in such cases get a plan or prepaid option from a mobile service provider or international specialist that works with UK plans. Some (virtual) international service providers have automatic eSIM switching for smart phones based on geolocation, so that you can use local data fees anywhere.

**Available at mobile phone stores/resellers (O2, Vodafone, EE, etc.). Probably even at UK international airports.

I assume that you are talking about an external Ethernet port?

You can get USB-C to Ethernet adapters. There are also many docks, including some small "travel docks", that have built-in Ethernet ports.

FWIW, I use this one when I travel with my Mac laptop: https://www.owc.com/solutions/usb-c-travel-dock-e