Help Code Signature invalid ,codesigning 0X1 can’t open GarageBand or iMovie high Sierra MBP 2010

Hi I recently got a MacBook Pro 2010 running high Sierra. From eBay it’s been very good

but I just installed GarageBand and iMovie and they won’t work .

when I downloaded them it said the current one would not work but gave me the option to download an earlier version so I Did.

when I start either of them they crash with a code signature invalid error ,codesign 0X1.

I googled and tried a number of solutions which included downloading a codesign app via terminal to manually sign them. I can’t find the page where I go the advice now . But the result was ,something was not present in the keychain ,and what had worked for some did not work for me . I have lost the page where I found the advice too now.

I also tried to start the app from the terminal or via safe mode . Neither of these remedied the problem.

safari runs ok ,as does chrome , also vlc streamer and amazing slow downer (a software for practicing music )

I really could use GarageBand and iMovie as I’m a guitar player hoping to start a YouTube channel

can anybody help me get these running please .

best regards a Paul. 🤘🏻🕶🤘🏻🎸🐆. 🎄