Your photos show two different types of paving; the top photo shows block paving, which is laid on sand with the blocks closely laid and then infilled with polymeric sand using a whacker plate. Whilst this type of paving is helpful to the environment because it's semi permeable (allows water to dissipate between the cracks, reducing flood risk from heavy rain generally) it does inevitably, over time, get weeds growing in between. It won't be possible to use a mortar mix to seal the gaps, particularly as it is not laid on hardcore beneath. In the UK, it's usual to apply a long acting path/driveway weedkiller such as Pathclear to the cracks in mid to late spring annually - this prevents growth for up to 4 months. This is done to avoid having to blast out in between gaps and reapply polymeric sand with a whacker plate (vibration plate), though this latter provides a much longer lasting solution.
The other paving looks as if its laid on soil, with large gaps between, If it has no harcore or concrete beneath, consider deliberately planting low growing plants in the gaps to prevent weed invasion. It depends on the climate where you live what type of plant you can use and to some extent how much foot traffic the area gets - clover will tolerate being walked over quite often, as will Soleirolia (or Helxine, sometimes known as mind your own business, see here https://www.rhs.org.uk/plants/17471/Soleirolia-soleirolii/Details) but there are other plants which can be used for lower traffic areas - see here for some suggestions https://www.flowerpotman.com/plants-for-soil-type-and-conditions/plants-for-pathways/.
UPDATE: GailD has not actually suggested just concrete, she is talking about a dry mortar mix, which is just sand and concrete well mixed together in a particular ratio. I have used this method myself with ordinary pavers spaced about quarter to half an inch apart, brushing it into the gaps, then gently pouring water over and it works well, assuming weather conditions are right. However, it's not clear whether you think you want to do that for the block paving, but bear in mind block paving is meant to interlock closely leaving a wafer thin gap in between each block which is not intended to have mortar between. The other answer suggests using a funnel to get the mortar mix in the gaps, but as I said before, a vibration plate is normally used because it's very difficult to get anything to go down in between the blocks.
As for the larger paving slabs, I would not use a dry mortar mix method there - the gaps are so wide that a wet mortar mix is fine. Regardless, wet or dry, I fear the gaps are so wide that the mortar, once set, will crack, especially as the material in between the slabs looks like loose, small chippings which presumably have not been compacted.