Why is Word suddenly running slow on my Mac running Big Sur?

Hi there. I have an old mac (12 inch retina 2015, running mac BigSur 11.7.10) and I can't upgrade to Monterey. Everything was working fine until a couple of days ago when suddenly word (16.77) started running super slow. Buying a new computer would be difficult: has anyone any idea why this happened or how to fix it? Thank you

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