yep only available once. Assuming the unable to travel due to covid extension isn't extended beyond 26 November then you'd need to either leave or switch to another visa.
You can't get a visa on arrival on a UK passport but you can get a 30 day visa exemption.
I don't know if you can apply for a 60 day tourist visa from India but if you can that will give you 3 months with the 30 day extension.
If you're spending nearly 50% of your time in Thailand then you may want to consider getting a more appropriate visa instead of relying on visa exemptions/tourist visas though.