Hi @James_Gould - thanks for your patience!
I'm having trouble reproducing this on my end, so I will need more info 
How did you want to store the value(s) in the database? Could you give me an example of what it should look like in the database if you select more than 1 option? Maybe DM me a screen recording of the values being saved?
It seems like you are storing the value with brackets because of the plus signs:
{{ '{' + keywordsInput10.value.toString() + '}' }} The plus signs join/concatenate onto your value, and if you remove them they won't be stored with the values you select.
Hope this helps! I would also recommend joining our live Zoom Community Office Hours on Tues and Thurs so we can troubleshoot together!
-Jen