Nintendo’s long-awaited Switch upgrade is expected to be shown ahead of E3 2021, according to a report published by Bloomberg [paywall] today and Eurogamer’s own sources.
I understand this is to ensure third-parties working on games which support the upgraded Switch are free to announce these projects at E3, and before Nintendo’s own digital showcase later in that week.
(Nintendo’s event has yet to be formally dated but is currently set to slot in after other publishers towards the end of E3, though of course dates can still shift.)