Stop complaining
In my view, looking at it from a different company, employees at Vodafone should stop complaining about this and stick to the extremely light rules on the office return.
A lot of other companies (say, BT as Telco ...without even mentioning Amazon as Tech) are pushing for way more than 2 days a week.
Vodafone pays relatively well, bonuses in Corporate are >3K (10% assumption for most of the cases), they also never reduced/cut any salaries/bonuses during COVID and always supported employees.
Also, this is the first time they are moving to this return model (considerably later than others, who adopted twice a week already around 2 years ago).
Also, a very uncomfortable true, for people complaining about space: Please let us know how many times you attended an office building on Mondays and Fridays (...I suspect not many, as strangely enough, there is usually a lot of space available on such days). The fact that these are not "popular days" it's a different story, but that's your "personal schedule story", not a company problem.
With this policy, VF still remain a perfectly viable option for flexibility and 100s times better than other Telco/Tech companies in the UK.
Also, individual circumstances can usually be agreed at HR level, when required (not for everyone, but for the extreme cases).
And, no, 2 days a week (which can be also done as 8 days altogether in a month) is definitely not a way to avoid bonus payments as I would expect >98% compliance with the policy, leaving 2% which is completely negligible in financial terms.