alternatively you could try a file picker extension...
the question is, if these still will work after App Inventor tagets SDK30...
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File Picker Plus Extension by Andres Daniel (12 USD) - web.archive.org link, Appybuilder community has been closed
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FileChooser Extension by Ben (10 USD) - web.archive.org link, Appybuilder community has been closed
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File Chooser Extension by Said Dev (10 EUR) - web.archive.org link, Appybuilder community has been closed
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File Explorer Extension by Kus Zab (free and 5 USD)
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2021-07
File Picker Extension Extension by JEWEL to pick file from storage
taken from the extensions directory https://puravidaapps.com/extensions.php
Taifun