Jumping in on the cancer and wisdom of mRNA Covid vaccines. As you likely recall when the vaccine was first available you had to be in a high risk category to get it. Cancer qualified you. Doctors while trained in science are not immune to political forces. You have at least two doctors who tell you to get the vaccine, one who is so tired I would speculate of arguing with patients about Covid that they have resorted to just giving the NIH handout (?CDC handout).
I found not a single reliable online recommendation to not receive the vaccine. Everything I read said that those actively being treated as well as those on long term treatment and those in remission all should be vaccinated. Some situations such as high dose steroids made it likely the vaccine would be less protective than in a non-cancer patient.
No one said don't get it. You have survived as the more lethal forms of Covid seem to have left circulation and those continuing to be here are less likely to hospitalize or kill. Like most people who drive drunk, don't wear seat belts, and run stop signs, survival is not evidence of having made good choices.
Mayo Clinic
Here
Cleveland Clinic
Here
MD Anderson
Here
Now ask that oncologist who said no, what is the reason, supported by the literature and expert opinion that lead that oncologist to tell you no and to continue to tell you no. Your originally posted question about whether you were at risk if mRNA was in a transfusion suggests to me that you have been getting really bad information about mRNA vaccines.