Not this old chestnut the Garda and GB border force share FULL disclosure of passenger manifests across the CTA and have done for many many years
Route through Dublin go land side and the Eire travel restrictions are enforced, connect onto the UK and you will be subject to the English or Scottish restrictions - Indeed make a false declaration and your going to be screwed.
Other than Lisbon where would you consider a possible market to use this dodge anyway.
Its not as through Dublin has an extensive range of long haul itself right now - 3 Aer Lingus US east coast, and a daily UA to Newark Air Canada to Toronto (where entry restrictions already exist at levels that make our red list laughable)