The log.txt lines tell me that there is a problem either with the processing of the master keys or there is some unhandled error immediately after those keys are loaded.
Now it's happening on my work machine. Same thing. Here's that screen shot you wanted, but it's from my work machine, not my home machine.
Spinning wheel on the CANCEL button. I can resize the GUI, minimize, maximize show no problems. CPU on the Joplin tasks are at 35% all night.
Last log.txt update was 12 hours ago, here are the last lines from it.
2021-07-01 18:18:37: "Sync: updateLocal: remote is more recent than local: Folder: (Local 79ea6d9b62af49f69b5ac46a8b6a4538): (Remote 79ea6d9b62af49f69b5ac46a8b6a4538.md)"
2021-07-01 18:18:38: "Sync: fetchingProcessed: Processing fetched item"
2021-07-01 18:18:38: "Sync: updateLocal: remote is more recent than local: Folder: (Local 78a0d2a648e94db3b4435d9d59769000): (Remote 78a0d2a648e94db3b4435d9d59769000.md)"
2021-07-01 18:18:39: "Sync: fetchingProcessed: Processing fetched item"
2021-07-01 18:18:39: "Sync: updateLocal: remote is more recent than local: Folder: (Local 038cab7750f64068a3d595fafa3214d4): (Remote 038cab7750f64068a3d595fafa3214d4.md)"
2021-07-01 18:18:40: "DecryptionWorker: completed decryption."
2021-07-01 18:18:40: "ResourceFetcher: Auto-add resources: Mode: always"
2021-07-01 18:18:40: "ResourceFetcher: Auto-added resources: 0"
2021-07-01 18:18:40: "Sync: fetchingProcessed: Processing fetched item"
2021-07-01 18:18:41: "Sync: updateLocal: remote is more recent than local: Folder: (Local 7aa0a0bed3c346d39f8586efc2bc286b): (Remote 7aa0a0bed3c346d39f8586efc2bc286b.md)"
2021-07-01 18:18:41: "DecryptionWorker: starting decryption..."
2021-07-01 18:18:42: "Sync: fetchingProcessed: Processing fetched item"
2021-07-01 18:18:42: "Sync: updateLocal: remote is more recent than local: Folder: (Local 565076c8843740b8b4700fd6c41e6c58): (Remote 565076c8843740b8b4700fd6c41e6c58.md)"
2021-07-01 18:18:44: "Sync: fetchingProcessed: Processing fetched item"
2021-07-01 18:18:44: "Sync: updateLocal: remote is more recent than local: Folder: (Local ee96b9bd7b5647d58d6e2866ff88ffd3): (Remote ee96b9bd7b5647d58d6e2866ff88ffd3.md)"
2021-07-01 18:18:45: "Sync: fetchingProcessed: Processing fetched item"
2021-07-01 18:18:45: "Sync: updateLocal: remote is more recent than local: Folder: (Local 3b9949b193014346b25c19c7677225fb): (Remote 3b9949b193014346b25c19c7677225fb.md)"
2021-07-01 18:18:47: "Sync: fetchingProcessed: Processing fetched item"
2021-07-01 18:18:47: "Sync: updateLocal: remote is more recent than local: Folder: (Local 29963745b58b4ff3bbaffc635fa11e0b): (Remote 29963745b58b4ff3bbaffc635fa11e0b.md)"
2021-07-01 18:18:47: "DecryptionWorker: completed decryption."
2021-07-01 18:18:48: "Sync: fetchingProcessed: Processing fetched item"
2021-07-01 18:18:48: "Sync: updateLocal: remote is more recent than local: Folder: (Local 4fe815c0a8a443fdbe75a48667fbaf2f): (Remote 4fe815c0a8a443fdbe75a48667fbaf2f.md)"
2021-07-01 18:18:48: "DecryptionWorker: starting decryption..."
It seems like the DecryptionWorker thread is hanging somehow.