I had a very similar experience. Pre-covid I would (according to my phone) walk 50-60 km a week mostly be just going about my day to day business. During covid I struggle to break 20km a week despite actively trying to go for walks.

I got a new job right as the pandemic started and also unfortunately stopped commuting by bike.

That combined with the uncertainty of even being near people outdoors for a few months killed the rhythm I had for mountain biking, hiking, and climbing. It took me about 9 months to adjust my food intake for this, and as a result I gained 15 pounds.

Luckily in the last three months I've gotten back on to a good active hobby schedule and adjusted my diet a bit and I'm just a few pounds above where I was!