If you're able to reliably replicate this bug with your own save file, then the very best thing you can do would be to submit it as a bug report to Larian directly, using their bug submission form, and include your save file (and the thumbnail image that is in its folder as well) in the submission as an attachment. Give them a step-by step on how to encounter the bug from loading the save.
You can find their official bug report form here:
https://larian.com/support/baldur-s-gate-3?ver=4.1.1.1233832#modal
