again, then Poland still had no Su-24 it could transfer, it only did the modifications
From what I understand Poland did not do the modifications but the modifications at least in part likely took place in Poland. It's speculation but with high plausibility.
Polish Air Force never used Su-24s so there's no know-how necessary to perform any modifications to the aircraft. What is highly likely however is that Poland provided the WZL2 facility in Bydgoszcz (Wojskowe Zakłady Lotnicze Nr.2, literally: military aerospace facility no.2) for Ukrainian and British specialists to perform modifications on a test airframe.
The reason for it is that WZL2 is the main maintenance and modernisation facility for Polish Air Force jet aircraft which includes MiG-29s. When Poland bought MiG-29s from USSR in the 1980s WZL2 has been given full documentation and toolset necessary to perform long-term maintenance of MiG-29s short of upgrades. The other maintenance set was sold to Czechoslovakia and Slovakia took it after the split but I'm not aware of the condition of the Slovak facility. WZL2 on the other hand performed maintenance of Bulgarian MiG-29s and offered similar services to other countries. It also performed minor upgrades to the MiGs in Polish AF service and was responsible for the overhaul of German MiG-29s after Poland took them in 2004.
Due to delays in procurement of new aircraft MiG-29s were retained in service in the squadrons at Mińsk Mazowiecki and Malbork. Not many aircraft were serviceable but the staff was kept on payroll so there were nominally two maintenance crews in both units and technicians at WZL. There were a few crashes in 2018 and 2019 and finally in early 2020 the government decided to order F-35s but before any decision on transition or retirement was made there came late 2021/early 2022 and everything was put on hold.
Then shortly after the beginning of Russia's invasion in 2022 a significant number of technical staff from Ukraine was moved to Poland to various facilities to establish a support network. In some cases entire technological chains were migrated for security reasons. Very quickly we've had news that MiGs are being worked on in WZL2 to be sent to Ukraine and later came the news of HARM integration which was in all likelihood performed in WZL2. Similarly engine maintenance etc is likely being done in Bydgoszcz.
And this means that WZL2 already has a working and tested team of Polish and Ukrainian specialists as well as American specialists working on various types of modifications for Ukrainian aircraft. With that already in place - and establishing working teams is always the biggest challenge - it would only require moving one or two Su-24 airframes to Bydgoszcz along with the relevant technical staff from Ukraine and Britain to do the work there on StormShadow integration. Everything else is in place including all the logistics for getting the airframes out of and back into Ukraine and the live testing could be done in secure conditions at of Polish AF testing grounds.
Other than that there's little that Poland can provide for Ukraine because apart from MiG-29s there's no common aircraft type used by both air forces and that means lack of know-how and personnel. Ukraine inherited standard Soviet complement and reduced it to four main types of latest models (Su-27, MiG-29, Su-24, Su-25) while Warsaw Pact countries had limited inventories of aircraft, mostly earlier designs like MiG-23, MiG-21, Su-22 etc. Su-27s and Su-24s were only used by Soviet Air Force. Su-25s were used in WP only by Bulgaria and Czechoslovakia but both Czechia and Slovakia sold their planes around 2000-04 which only leaves Bulgaria with expertise in maintenance of this type.
Hopefully this provided some much needed context. Social media is little more than a race to the bottom for the greatest number of shares and likes.
