Some "planners" are saying that fare-free public transit will lead to less walking and cycling. Here is a study from VTPI that show that public transit increases physical activity. Some excerpts:
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Since active transport (walking and cycling) and public transit are complements, transit travel tends to increase public fitness and health.
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The 2004 American Community Survey found that consumers place a high value on urban amenities such as shorter commute time and neighborhood walkability: 60% of prospective homebuyers surveyed reported that they prefer a neighborhood that offered a shorter commute, sidewalks and amenities like local shops, restaurants, libraries, schools and public transport over a more automobile-dependent community
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Described differently, high quality transit requires an integrated system that includes attractive stops and stations surrounded by compact and mixed development, good walking and bicycling conditions, reduced parking supply, and more social acceptance of non-auto travel;
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Residents of transit-oriented developments tend to own about half as many vehicles, generate half as many vehicle trips, and rely on walking, cycling and public transit much more than in automobile-dependent communities (Arrington and Sloop 2009).
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Similarly, Wedderburn (2013) found that in New Zealand urban areas, each additional daily transit trip by driving age (18+ years) residents is associated with 0.95 more walking trips and 1.21 kilometers (in addition to the walking trips to access transit), and reductions of two daily car driver trips and 45 vehicle-kms, approximately 5 kilometers of reduced vehicle travel for each additional transit passenger-km.
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Inadequate physical activity contributes to cardiovascular disease, diabetes, hypertension, obesity, osteoporosis and some cancers. Many experts consider increased walking and cycling for daily transport one of the most practical ways to increase public fitness and health (AJHP 2003). Most transit trips include walking or cycling links, so transit travel tends to increase physical activity (Devries, et al. 2018; Edwards 2008; Frank, et al. 2010; Litman 2010b). Public transit users average about three times as much walking as people who rely on automobile transport, nearly achieving the 22 daily minutes of moderate physical activity considered necessary for health (Besser and Dannenberg 2005; Weinstein and Schimek 2005; Wener and Evans 2007). Lachapelle, et al. (2011) found that transit commuters average 5 to 10 more daily minutes of moderate-intensity physical activity, and walked more to local services
