not touchy....just wondering why you mention land entries in first place. OP is talking about doing runs to KL and Singapore; much easier done by air than land.
I didnt once mention anything about land entries.....as for air entries can you please direct me to the reference for 4 allowed entries before being questioned? Cheers.
while there are no restrictions on number of 30-day visa exemption entries by air, you run the risk of being stopped at IC if they see back to back to back use of this.
perhaps look into applying for the Covid extension of stay (currently able to apply until July 25 I think). If will either be approved or denied - in which case a notice to leave of 7 days is given. As
I think the legal implications would still be the same, whether or not the last day of stay is a Sunday. OP is permitted (I believe) to cancel work permit in advance (not sure how many days). Even if they go in ahead of time, the date of cancellation will be marked as the last day of extension of stay, not the day OP goes in. Best to cancel everything legally if there is a chance of returning at some point in the future.
OP already has visa issued. No need to visit country in any country - I would imagine entering country X is sufficient, then turning around and coming straight back to Thailand with the already-approved visa.