No. It is Marxist. I'm startled that this is even a question.

UBI is just a redistributive measure in order to justify further commodification of public services.

The 4 day work week is in line with the historic proposals of the communists for a reduction in working hours, together with an increase in minimum wage.

Basically, productivity (per person-workhour) has gone up for the past 100 years since the 5 day 8 hour work week was normalised, but workers still receive a pittance of a wage and work the same amount of time. Since that increased value must be going somewhere, it's going into the surplus value (profits) of the businesses. That means that capital owners are earning more, while the workers are earning the same or even less for their time.

An enforced obligatory 4 day work week (with no wage reduction) would imply in a 20% increase in valuation for the working hour. The conditions over whether this is a worthwhile struggle in your region depends on a lot of factors (I.e. I think in the US people are paid by the hour rather than monthly), but instituting high minimum wages and low maximum working hours are essential since companies will tend to those minimums and maximums.

Since the end goal of Marxism is the elimination of surplus extraction, rejecting workweek reduction out of hand would be absurd.

I know Capital is a handful, but please at least give Wage Labour and Capital and Value Price and Profit a quick read. It'll take two hours at most and probably elucidate the principles by which Marxists choose reforms to support.