There are adequate examples for SSD upgrade, including external; to run later macOS from there.
And these can be optioned with enclosures; either to swap internal SSD, or run new one
externally. Options could include 'port-powered USB' ~ or AC-powered enclosure.
[MacTracker shows yours as 2018 model, that may have replaceable SSD, other resources show it
as 2019 model; OWC groups the 2018 with 2017 as replaceable, or with 2019 on newer fringe that
would require external SSD upgrade within an enclosure; & use any upgrade external to leave OEM
hardware alone; boot from second drive to run. MacTracker shows 2018 as 8.0 GT/s NVMe PCIe x4]
• Upgrades guaranteed to work with your Mac | OWC (including external SSD enclosures)
https://eshop.macsales.com/upgrades/macbook-air-13-inch-mid-2019-1.6-ghz
Bus powered & portable SSD examples, part of larger selection linked from OWC storage pages.
https://eshop.macsales.com/upgrades/macbook-air-13-inch-mid-2019-1.6-ghz/ExternalStorage?&filter.dimension_bus_powered_portable_160=Bus%2DPowered%20/%20Portable#top-of-results
{Mac-centric eseller has good examples of update/upgrade hardware; good attention
to full service before + after sale. Among masters of 'remote support' pre-pandemic.}
..Good luck & happy computing.!
🌿⛵️🎣🌻🌤🌎🌙🌞🐝😳🐶